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Precalculus

12.1 Finding Limits: Numerical and Graphical Approaches

Precalculus12.1 Finding Limits: Numerical and Graphical Approaches
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  1. Preface
  2. 1 Functions
    1. Introduction to Functions
    2. 1.1 Functions and Function Notation
    3. 1.2 Domain and Range
    4. 1.3 Rates of Change and Behavior of Graphs
    5. 1.4 Composition of Functions
    6. 1.5 Transformation of Functions
    7. 1.6 Absolute Value Functions
    8. 1.7 Inverse Functions
    9. Key Terms
    10. Key Equations
    11. Key Concepts
    12. Review Exercises
    13. Practice Test
  3. 2 Linear Functions
    1. Introduction to Linear Functions
    2. 2.1 Linear Functions
    3. 2.2 Graphs of Linear Functions
    4. 2.3 Modeling with Linear Functions
    5. 2.4 Fitting Linear Models to Data
    6. Key Terms
    7. Key Equations
    8. Key Concepts
    9. Review Exercises
    10. Practice Test
  4. 3 Polynomial and Rational Functions
    1. Introduction to Polynomial and Rational Functions
    2. 3.1 Complex Numbers
    3. 3.2 Quadratic Functions
    4. 3.3 Power Functions and Polynomial Functions
    5. 3.4 Graphs of Polynomial Functions
    6. 3.5 Dividing Polynomials
    7. 3.6 Zeros of Polynomial Functions
    8. 3.7 Rational Functions
    9. 3.8 Inverses and Radical Functions
    10. 3.9 Modeling Using Variation
    11. Key Terms
    12. Key Equations
    13. Key Concepts
    14. Review Exercises
    15. Practice Test
  5. 4 Exponential and Logarithmic Functions
    1. Introduction to Exponential and Logarithmic Functions
    2. 4.1 Exponential Functions
    3. 4.2 Graphs of Exponential Functions
    4. 4.3 Logarithmic Functions
    5. 4.4 Graphs of Logarithmic Functions
    6. 4.5 Logarithmic Properties
    7. 4.6 Exponential and Logarithmic Equations
    8. 4.7 Exponential and Logarithmic Models
    9. 4.8 Fitting Exponential Models to Data
    10. Key Terms
    11. Key Equations
    12. Key Concepts
    13. Review Exercises
    14. Practice Test
  6. 5 Trigonometric Functions
    1. Introduction to Trigonometric Functions
    2. 5.1 Angles
    3. 5.2 Unit Circle: Sine and Cosine Functions
    4. 5.3 The Other Trigonometric Functions
    5. 5.4 Right Triangle Trigonometry
    6. Key Terms
    7. Key Equations
    8. Key Concepts
    9. Review Exercises
    10. Practice Test
  7. 6 Periodic Functions
    1. Introduction to Periodic Functions
    2. 6.1 Graphs of the Sine and Cosine Functions
    3. 6.2 Graphs of the Other Trigonometric Functions
    4. 6.3 Inverse Trigonometric Functions
    5. Key Terms
    6. Key Equations
    7. Key Concepts
    8. Review Exercises
    9. Practice Test
  8. 7 Trigonometric Identities and Equations
    1. Introduction to Trigonometric Identities and Equations
    2. 7.1 Solving Trigonometric Equations with Identities
    3. 7.2 Sum and Difference Identities
    4. 7.3 Double-Angle, Half-Angle, and Reduction Formulas
    5. 7.4 Sum-to-Product and Product-to-Sum Formulas
    6. 7.5 Solving Trigonometric Equations
    7. 7.6 Modeling with Trigonometric Equations
    8. Key Terms
    9. Key Equations
    10. Key Concepts
    11. Review Exercises
    12. Practice Test
  9. 8 Further Applications of Trigonometry
    1. Introduction to Further Applications of Trigonometry
    2. 8.1 Non-right Triangles: Law of Sines
    3. 8.2 Non-right Triangles: Law of Cosines
    4. 8.3 Polar Coordinates
    5. 8.4 Polar Coordinates: Graphs
    6. 8.5 Polar Form of Complex Numbers
    7. 8.6 Parametric Equations
    8. 8.7 Parametric Equations: Graphs
    9. 8.8 Vectors
    10. Key Terms
    11. Key Equations
    12. Key Concepts
    13. Review Exercises
    14. Practice Test
  10. 9 Systems of Equations and Inequalities
    1. Introduction to Systems of Equations and Inequalities
    2. 9.1 Systems of Linear Equations: Two Variables
    3. 9.2 Systems of Linear Equations: Three Variables
    4. 9.3 Systems of Nonlinear Equations and Inequalities: Two Variables
    5. 9.4 Partial Fractions
    6. 9.5 Matrices and Matrix Operations
    7. 9.6 Solving Systems with Gaussian Elimination
    8. 9.7 Solving Systems with Inverses
    9. 9.8 Solving Systems with Cramer's Rule
    10. Key Terms
    11. Key Equations
    12. Key Concepts
    13. Review Exercises
    14. Practice Test
  11. 10 Analytic Geometry
    1. Introduction to Analytic Geometry
    2. 10.1 The Ellipse
    3. 10.2 The Hyperbola
    4. 10.3 The Parabola
    5. 10.4 Rotation of Axes
    6. 10.5 Conic Sections in Polar Coordinates
    7. Key Terms
    8. Key Equations
    9. Key Concepts
    10. Review Exercises
    11. Practice Test
  12. 11 Sequences, Probability and Counting Theory
    1. Introduction to Sequences, Probability and Counting Theory
    2. 11.1 Sequences and Their Notations
    3. 11.2 Arithmetic Sequences
    4. 11.3 Geometric Sequences
    5. 11.4 Series and Their Notations
    6. 11.5 Counting Principles
    7. 11.6 Binomial Theorem
    8. 11.7 Probability
    9. Key Terms
    10. Key Equations
    11. Key Concepts
    12. Review Exercises
    13. Practice Test
  13. 12 Introduction to Calculus
    1. Introduction to Calculus
    2. 12.1 Finding Limits: Numerical and Graphical Approaches
    3. 12.2 Finding Limits: Properties of Limits
    4. 12.3 Continuity
    5. 12.4 Derivatives
    6. Key Terms
    7. Key Equations
    8. Key Concepts
    9. Review Exercises
    10. Practice Test
  14. A | Basic Functions and Identities
  15. Answer Key
    1. Chapter 1
    2. Chapter 2
    3. Chapter 3
    4. Chapter 4
    5. Chapter 5
    6. Chapter 6
    7. Chapter 7
    8. Chapter 8
    9. Chapter 9
    10. Chapter 10
    11. Chapter 11
    12. Chapter 12
  16. Index

Learning Objectives

In this section, you will:
  • Understand limit notation.
  • Find a limit using a graph.
  • Find a limit using a table.

Intuitively, we know what a limit is. A car can go only so fast and no faster. A trash can might hold 33 gallons and no more. It is natural for measured amounts to have limits. What, for instance, is the limit to the height of a woman? The tallest woman on record was Jinlian Zeng from China, who was 8 ft 1 in.36 Is this the limit of the height to which women can grow? Perhaps not, but there is likely a limit that we might describe in inches if we were able to determine what it was.

To put it mathematically, the function whose input is a woman and whose output is a measured height in inches has a limit. In this section, we will examine numerical and graphical approaches to identifying limits.

Understanding Limit Notation

We have seen how a sequence can have a limit, a value that the sequence of terms moves toward as the nu mber of terms increases. For example, the terms of the sequence

1, 1 2 , 1 4 , 1 8 ... 1, 1 2 , 1 4 , 1 8 ...

gets closer and closer to 0. A sequence is one type of function, but functions that are not sequences can also have limits. We can describe the behavior of the function as the input values get close to a specific value. If the limit of a function f(x)=L, f(x)=L, then as the input x xgets closer and closer to a, a, the output y-coordinate gets closer and closer to L. L. We say that the output “approaches” L. L.

Figure 1 provides a visual representation of the mathematical concept of limit. As the input value x xapproaches a, a, the output value f( x ) f( x ) approaches L. L.

Graph representing how a function with a hole at (a, L) approaches a limit.
Figure 1 The output (y--coordinate) approaches L Las the input (x-coordinate) approaches a. a.

We write the equation of a limit as

lim xa f(x)=L. lim xa f(x)=L.

This notation indicates that as x xapproaches a aboth from the left of x=a x=a and the right of x=a, x=a, the output value approaches L. L.

Consider the function

f(x)= x 2 6x7 x7 . f(x)= x 2 6x7 x7 .

We can factor the function as shown.

f(x)= (x7) (x+1) x7   Cancel like factors in numerator and denominator. f(x)=x+1,x7 Simplify. f(x)= (x7) (x+1) x7   Cancel like factors in numerator and denominator. f(x)=x+1,x7 Simplify.

Notice that x xcannot be 7, or we would be dividing by 0, so 7 is not in the domain of the original function. In order to avoid changing the function when we simplify, we set the same condition, x7, x7, for the simplified function. We can represent the function graphically as shown in Figure 2.

Graph of an increasing function, f(x) = (x^2-6x-7)/(x-7), with a hole at (7, 8).
Figure 2 Because 7 is not allowed as an input, there is no point at x=7. x=7.

What happens at x=7 x=7 is completely different from what happens at points close to x=7 x=7 on either side. The notation

lim x7 f(x)=8 lim x7 f(x)=8

indicates that as the input x xapproaches 7 from either the left or the right, the output approaches 8. The output can get as close to 8 as we like if the input is sufficiently near 7.

What happens at x=7? x=7? When x=7, x=7, there is no corresponding output. We write this as

f(7) does not exist. f(7) does not exist.

This notation indicates that 7 is not in the domain of the function. We had already indicated this when we wrote the function as

f(x)=x+1,  x7. f(x)=x+1,  x7.

Notice that the limit of a function can exist even when f(x) f(x) is not defined at x=a. x=a. Much of our subsequent work will be determining limits of functions as x xnears a, a, even though the output at x=a x=a does not exist.

The Limit of a Function

A quantity L Lis the limit of a function f( x ) f( x ) as x xapproaches a aif, as the input values of x xapproach a a(but do not equal a), a), the corresponding output values of f( x ) f( x ) get closer to L. L. Note that the value of the limit is not affected by the output value of f( x ) f( x ) at a. a. Both a aand L Lmust be real numbers. We write it as

lim xa f(x)=L lim xa f(x)=L

Example 1

Understanding the Limit of a Function

For the following limit, define a,f(x), a,f(x), and L. L.

lim x2 ( 3x+5 )=11 lim x2 ( 3x+5 )=11

Analysis

Recall that y=3x+5 y=3x+5 is a line with no breaks. As the input values approach 2, the output values will get close to 11. This may be phrased with the equation lim x2 (3x+5)=11 , lim x2 (3x+5)=11 , which means that as x xnears 2 (but is not exactly 2), the output of the function f(x)=3x+5 f(x)=3x+5 gets as close as we want to 3(2)+5, 3(2)+5, or 11, which is the limit L, L, as we take values of x xsufficiently near 2 but not at x=2. x=2.

Try It #1

For the following limit, define a,f(x), a,f(x), and L. L.

lim x5 ( 2 x 2 4 )=46 lim x5 ( 2 x 2 4 )=46

Understanding Left-Hand Limits and Right-Hand Limits

We can approach the input of a function from either side of a value—from the left or the right. Figure 3 shows the values of

f(x)=x+1,x7 f(x)=x+1,x7

as described earlier and depicted in Figure 2.

Table showing that f(x) approaches 8 from either side as x approaches 7 from either side.
Figure 3

Values described as “from the left” are less than the input value 7 and would therefore appear to the left of the value on a number line. The input values that approach 7 from the left in Figure 3 are 6.9, 6.9, 6.99, 6.99, and 6.999. 6.999. The corresponding outputs are 7.9,7.99, 7.9,7.99, and 7.999. 7.999. These values are getting closer to 8. The limit of values of f( x ) f( x ) as x xapproaches from the left is known as the left-hand limit. For this function, 8 is the left-hand limit of the function f(x)=x+1,x7 f(x)=x+1,x7 as x xapproaches 7.

Values described as “from the right” are greater than the input value 7 and would therefore appear to the right of the value on a number line. The input values that approach 7 from the right in Figure 3 are 7.1, 7.1, 7.01, 7.01, and 7.001. 7.001. The corresponding outputs are 8.1, 8.1, 8.01, 8.01, and 8.001. 8.001. These values are getting closer to 8. The limit of values of f( x ) f( x ) as x xapproaches from the right is known as the right-hand limit. For this function, 8 is also the right-hand limit of the function f(x)=x+1,x7 f(x)=x+1,x7 as x xapproaches 7.

Figure 3 shows that we can get the output of the function within a distance of 0.1 from 8 by using an input within a distance of 0.1 from 7. In other words, we need an input x xwithin the interval 6.9<x<7.1 6.9<x<7.1 to produce an output value of f( x ) f( x ) within the interval 7.9<f(x)<8.1. 7.9<f(x)<8.1.

We also see that we can get output values of f(x) f(x) successively closer to 8 by selecting input values closer to 7. In fact, we can obtain output values within any specified interval if we choose appropriate input values.

Figure 4 provides a visual representation of the left- and right-hand limits of the function. From the graph of f(x), f(x), we observe the output can get infinitesimally close to L=8 L=8 as x xapproaches 7 from the left and as x xapproaches 7 from the right.

To indicate the left-hand limit, we write

lim x 7 f(x)=8. lim x 7 f(x)=8.

To indicate the right-hand limit, we write

lim x 7 + f(x)=8. lim x 7 + f(x)=8.
Graph of the previous function explaining the function's limit at (7, 8)
Figure 4 The left- and right-hand limits are the same for this function.

Left- and Right-Hand Limits

The left-hand limit of a function f(x) f(x) as x xapproaches a afrom the left is equal to L, L, denoted by

lim x a f(x)=L. lim x a f(x)=L.

The values of f(x) f(x) can get as close to the limit L Las we like by taking values of x xsufficiently close to a asuch that x<a x<a and xa. xa.

The right-hand limit of a function f(x), f(x), as x xapproaches a afrom the right, is equal to L, L, denoted by

lim x a + f(x)=L. lim x a + f(x)=L.

The values of f(x) f(x) can get as close to the limit L Las we like by taking values of x xsufficiently close to a abut greater than a. a. Both a aand L Lare real numbers.

Understanding Two-Sided Limits

In the previous example, the left-hand limit and right-hand limit as x xapproaches a aare equal. If the left- and right-hand limits are equal, we say that the function f(x) f(x) has a two-sided limit as x xapproaches a. a. More commonly, we simply refer to a two-sided limit as a limit. If the left-hand limit does not equal the right-hand limit, or if one of them does not exist, we say the limit does not exist.

The Two-Sided Limit of Function as x Approaches a

The limit of a function f(x), f(x), as x xapproaches a, a, is equal to L, L, that is,

lim xa f(x)=L lim xa f(x)=L

if and only if

lim x a f(x)= lim x a + f(x). lim x a f(x)= lim x a + f(x).

In other words, the left-hand limit of a function f(x) f(x) as x xapproaches a ais equal to the right-hand limit of the same function as x xapproaches a. a. If such a limit exists, we refer to the limit as a two-sided limit. Otherwise we say the limit does not exist.

Finding a Limit Using a Graph

To visually determine if a limit exists as x xapproaches a, a, we observe the graph of the function when x xis very near to x=a. x=a. In Figure 5 we observe the behavior of the graph on both sides of a. a.

Graph of a function that explains the behavior of a limit at (a, L) where the function is increasing when x is less than a and decreasing when x is greater than a.
Figure 5

To determine if a left-hand limit exists, we observe the branch of the graph to the left of x=a, x=a, but near x=a. x=a. This is where x<a. x<a. We see that the outputs are getting close to some real number L Lso there is a left-hand limit.

To determine if a right-hand limit exists, observe the branch of the graph to the right of x=a, x=a, but near x=a. x=a. This is where x>a. x>a. We see that the outputs are getting close to some real number L, L, so there is a right-hand limit.

If the left-hand limit and the right-hand limit are the same, as they are in Figure 5, then we know that the function has a two-sided limit. Normally, when we refer to a “limit,” we mean a two-sided limit, unless we call it a one-sided limit.

Finally, we can look for an output value for the function f( x ) f( x ) when the input value x xis equal to a. a. The coordinate pair of the point would be ( a,f( a ) ). ( a,f( a ) ). If such a point exists, then f( a ) f( a ) has a value. If the point does not exist, as in Figure 5, then we say that f( a ) f( a ) does not exist.

How To

Given a function f( x ), f( x ), use a graph to find the limits and a function value as x xapproaches a. a.

  1. Examine the graph to determine whether a left-hand limit exists.
  2. Examine the graph to determine whether a right-hand limit exists.
  3. If the two one-sided limits exist and are equal, then there is a two-sided limit—what we normally call a “limit.”
  4. If there is a point at x=a, x=a, then f( a ) f( a ) is the corresponding function value.

Example 2

Finding a Limit Using a Graph

  1. Determine the following limits and function value for the function f fshown in Figure 6.
    1. lim x 2 f(x) lim x 2 f(x)
    2. lim x 2 + f(x) lim x 2 + f(x)
    3. lim x2 f(x) lim x2 f(x)
    4. f(2) f(2)
    Graph of a piecewise function that has a positive parabola centered at the origin and goes from negative infinity to (2, 8), an open point, and a decreasing line from (2, 3), a closed point, to positive infinity on the x-axis.
    Figure 6
  2. Determine the following limits and function value for the function f fshown in Figure 7.
    1. lim x 2 f(x) lim x 2 f(x)
    2. lim x 2 + f(x) lim x 2 + f(x)
    3. lim x2 f(x) lim x2 f(x)
    4. f(2) f(2)
    Graph of a piecewise function that has a positive parabola from negative infinity to 2 on the x-axis, a decreasing line from 2 to positive infinity on the x-axis, and a point at (2, 4).
    Figure 7
Try It #2

Using the graph of the function y=f( x ) y=f( x ) shown in Figure 8, estimate the following limits.

Graph of a piecewise function that has three segments: 1) negative infinity to 0, 2) 0 to 2, and 3) 2 to positive inifnity, which has a discontinuity at (4, 4)
Figure 8

Finding a Limit Using a Table

Creating a table is a way to determine limits using numeric information. We create a table of values in which the input values of x xapproach a afrom both sides. Then we determine if the output values get closer and closer to some real value, the limit L. L.

Let’s consider an example using the following function:

lim x5 ( x 3 125 x5 ) lim x5 ( x 3 125 x5 )

To create the table, we evaluate the function at values close to x=5. x=5. We use some input values less than 5 and some values greater than 5 as in Figure 9. The table values show that when x>5 x>5 but nearing 5, the corresponding output gets close to 75. When x>5 x>5 but nearing 5, the corresponding output also gets close to 75.

Table shows that as x values approach 5 from the positive or negative direction, f(x) gets very close to 75. But when x is equal to 5, y is undefined.
Figure 9

Because

lim x 5 f(x)=75= lim x 5 + f(x), lim x 5 f(x)=75= lim x 5 + f(x),

then

lim x5 f(x)=75. lim x5 f(x)=75.

Remember that f( 5 ) f( 5 ) does not exist.

How To

Given a function f, f, use a table to find the limit as x xapproaches a aand the value of f(a), f(a), if it exists.

  1. Choose several input values that approach a afrom both the left and right. Record them in a table.
  2. Evaluate the function at each input value. Record them in the table.
  3. Determine if the table values indicate a left-hand limit and a right-hand limit.
  4. If the left-hand and right-hand limits exist and are equal, there is a two-sided limit.
  5. Replace x xwith a ato find the value of f( a ). f( a ).

Example 3

Finding a Limit Using a Table

Numerically estimate the limit of the following expression by setting up a table of values on both sides of the limit.

lim x0 ( 5sin(x) 3x ) lim x0 ( 5sin(x) 3x )

Q&A

Is it possible to check our answer using a graphing utility?

Yes. We previously used a table to find a limit of 75 for the function f(x)= x 3 125 x5 f(x)= x 3 125 x5 as x xapproaches 5. To check, we graph the function on a viewing window as shown in Figure 11. A graphical check shows both branches of the graph of the function get close to the output 75 as x xnears 5. Furthermore, we can use the ‘trace’ feature of a graphing calculator. By appraoching x=5 x=5 we may numerically observe the corresponding outputs getting close to 75. 75.

Graph of an increasing function with a discontinuity at (5, 75)
Figure 11
Try It #3

Numerically estimate the limit of the following function by making a table:

lim x0 ( 20sin(x) 4x ) lim x0 ( 20sin(x) 4x )

Q&A

Is one method for determining a limit better than the other?

No. Both methods have advantages. Graphing allows for quick inspection. Tables can be used when graphical utilities aren’t available, and they can be calculated to a higher precision than could be seen with an unaided eye inspecting a graph.

Example 4

Using a Graphing Utility to Determine a Limit

With the use of a graphing utility, if possible, determine the left- and right-hand limits of the following function as x xapproaches 0. If the function has a limit as x xapproaches 0, state it. If not, discuss why there is no limit.

f(x)=3sin( π x ) f(x)=3sin( π x )
Try It #4

Numerically estimate the following limit: lim x0 ( sin( 2 x ) ). lim x0 ( sin( 2 x ) ).

Media

Access these online resources for additional instruction and practice with finding limits.

Footnotes

  • 36 https://en.wikipedia.org/wiki/Human_height and http://en.wikipedia.org/wiki/List_of_tallest_people

12.1 Section Exercises

Verbal

1.

Explain the difference between a value at x=a x=a and the limit as x xapproaches a. a.

2.

Explain why we say a function does not have a limit as x xapproaches a aif, as x xapproaches a, a, the left-hand limit is not equal to the right-hand limit.

Graphical

For the following exercises, estimate the functional values and the limits from the graph of the function f fprovided in Figure 14.

A piecewise function with discontinuities at x = -2, x = 1, and x = 4.
Figure 14
3.

lim x 2 f(x) lim x 2 f(x)

4.

lim x 2 + f(x) lim x 2 + f(x)

5.

lim x2 f(x) lim x2 f(x)

6.

f(−2) f(−2)

7.

lim x 1 f(x) lim x 1 f(x)

8.

lim x 1 + f(x) lim x 1 + f(x)

9.

lim x1 f(x) lim x1 f(x)

10.

f(1) f(1)

11.

lim x 4 f(x) lim x 4 f(x)

12.

lim x 4 + f(x) lim x 4 + f(x)

13.

lim x4 f(x) lim x4 f(x)

14.

f(4) f(4)

For the following exercises, draw the graph of a function from the functional values and limits provided.

15.

lim x 0 f(x)=2, lim x 0 + f(x)=3, lim x2 f(x)=2,f(0)=4,f(2)=1,f(3) does not exist. lim x 0 f(x)=2, lim x 0 + f(x)=3, lim x2 f(x)=2,f(0)=4,f(2)=1,f(3) does not exist.

16.

lim x 2 f(x)=0, lim x 2 + =2, lim x0 f(x)=3,f(2)=5,f(0) lim x 2 f(x)=0, lim x 2 + =2, lim x0 f(x)=3,f(2)=5,f(0)

17.

lim x 2 f(x)=2, lim x 2 + f(x)=3, lim x0 f(x)=5,f(0)=1,f(1)=0 lim x 2 f(x)=2, lim x 2 + f(x)=3, lim x0 f(x)=5,f(0)=1,f(1)=0

18.

lim x 3 f(x)=0, lim x 3 + f(x)=5, lim x5 f(x)=0,f(5)=4,f(3) does not exist. lim x 3 f(x)=0, lim x 3 + f(x)=5, lim x5 f(x)=0,f(5)=4,f(3) does not exist.

19.

lim x4 f(x)=6, lim x 6 + f(x)=1, lim x0 f(x)=5,f(4)=6,f(2)=6 lim x4 f(x)=6, lim x 6 + f(x)=1, lim x0 f(x)=5,f(4)=6,f(2)=6

20.

lim x3 f(x)=2, lim x 1 + f(x)=2, lim x3 f(x)=4,f(3)=0,f(0)=0 lim x3 f(x)=2, lim x 1 + f(x)=2, lim x3 f(x)=4,f(3)=0,f(0)=0

21.

lim xπ f(x)= π 2 , lim xπ f(x)= π 2 , lim x 1 f(x)=0,f(π)= 2 ,f(0) does not exist. lim xπ f(x)= π 2 , lim xπ f(x)= π 2 , lim x 1 f(x)=0,f(π)= 2 ,f(0) does not exist.

For the following exercises, use a graphing calculator to determine the limit to 5 decimal places as x xapproaches 0.

22.

f(x)= ( 1+x ) 1 x f(x)= ( 1+x ) 1 x

23.

g(x)= ( 1+x ) 2 x g(x)= ( 1+x ) 2 x

24.

h(x)= ( 1+x ) 3 x h(x)= ( 1+x ) 3 x

25.

i(x)= ( 1+x ) 4 x i(x)= ( 1+x ) 4 x

26.

j(x)= ( 1+x ) 5 x j(x)= ( 1+x ) 5 x

27.

Based on the pattern you observed in the exercises above, make a conjecture as to the limit of f(x)= ( 1+x ) 6 x , f(x)= ( 1+x ) 6 x , g(x)= ( 1+x ) 7 x , g(x)= ( 1+x ) 7 x , and h(x)= ( 1+x ) n x . and h(x)= ( 1+x ) n x .

For the following exercises, use a graphing utility to find graphical evidence to determine the left- and right-hand limits of the function given as x xapproaches a. a. If the function has a limit as x xapproaches a, a, state it. If not, discuss why there is no limit.

28.

(x)={ | x |1, if x1 x 3 , if x=1  a=1 (x)={ | x |1, if x1 x 3 , if x=1  a=1

29.

(x)={ 1 x+1 , if x=2 (x+1) 2 , if x2  a=2 (x)={ 1 x+1 , if x=2 (x+1) 2 , if x2  a=2

Numeric

For the following exercises, use numerical evidence to determine whether the limit exists at x=a. x=a. If not, describe the behavior of the graph of the function near x=a. x=a. Round answers to two decimal places.

30.

f(x)= x 2 4x 16 x 2 ;a=4 f(x)= x 2 4x 16 x 2 ;a=4

31.

f(x)= x 2 x6 x 2 9 ;a=3 f(x)= x 2 x6 x 2 9 ;a=3

32.

f(x)= x 2 6x7 x 2  7x ;a=7 f(x)= x 2 6x7 x 2  7x ;a=7

33.

f(x)= x 2 1 x 2 3x+2 ;a=1 f(x)= x 2 1 x 2 3x+2 ;a=1

34.

f(x)= 1 x 2 x 2 3x+2 ;a=1 f(x)= 1 x 2 x 2 3x+2 ;a=1

35.

f(x)= 1010 x 2 x 2 3x+2 ;a=1 f(x)= 1010 x 2 x 2 3x+2 ;a=1

36.

f(x)= x 6 x 2 5x6 ;a= 3 2 f(x)= x 6 x 2 5x6 ;a= 3 2

37.

f(x)= x 4 x 2 +4x+1 ;a= 1 2 f(x)= x 4 x 2 +4x+1 ;a= 1 2

38.

f(x)= 2 x4 ; a=4 f(x)= 2 x4 ; a=4

For the following exercises, use a calculator to estimate the limit by preparing a table of values. If there is no limit, describe the behavior of the function as x xapproaches the given value.

39.

lim x0 7tanx 3x lim x0 7tanx 3x

40.

lim x4 x 2 x4 lim x4 x 2 x4

41.

lim x0 2sinx 4tanx lim x0 2sinx 4tanx

For the following exercises, use a graphing utility to find numerical or graphical evidence to determine the left and right-hand limits of the function given as x xapproaches a. a. If the function has a limit as x xapproaches a, a, state it. If not, discuss why there is no limit.

42.

lim x0 e e 1 x lim x0 e e 1 x

43.

lim x0 e e   1 x 2 lim x0 e e   1 x 2

44.

lim x0 | x | x lim x0 | x | x

45.

lim x1 | x+1 | x+1 lim x1 | x+1 | x+1

46.

lim x5 | x5 | 5x lim x5 | x5 | 5x

47.

lim x1 1 ( x+1 ) 2 lim x1 1 ( x+1 ) 2

48.

lim x1 1 ( x1 ) 3 lim x1 1 ( x1 ) 3

49.

lim x0 5 1 e 2 x lim x0 5 1 e 2 x

50.

Use numerical and graphical evidence to compare and contrast the limits of two functions whose formulas appear similar: f(x)=| 1x x | f(x)=| 1x x | and g(x)=| 1+x x | g(x)=| 1+x x | as x xapproaches 0. Use a graphing utility, if possible, to determine the left- and right-hand limits of the functions f( x ) f( x ) and g( x ) g( x ) as x xapproaches 0. If the functions have a limit as x xapproaches 0, state it. If not, discuss why there is no limit.

Extensions

51.

According to the Theory of Relativity, the mass m mof a particle depends on its velocity v v. That is

m= m o 1( v 2 / c 2 ) m= m o 1( v 2 / c 2 )

where m o m o is the mass when the particle is at rest and c cis the speed of light. Find the limit of the mass, m, m, as v vapproaches c . c .

52.

Allow the speed of light, c, c, to be equal to 1.0. If the mass, m, m, is 1, what occurs to m mas vc? vc? Using the values listed in Table 1, make a conjecture as to what the mass is as v vapproaches 1.00.

vv mm
0.51.15
0.92.29
0.953.20
0.997.09
0.99922.36
0.99999223.61
Table 1
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