Activity
Here is a pattern of squares.
1. Is the number of small squares growing linearly? Explain how you know.
Compare your answer:
No, there are 3 squares in the first step, 6 squares in the second step, and 11 squares in the third step. So the number of additional squares is 3 going from the first to the second step and 5 going from the second to the third step.
2. Answer questions a–e to complete the table.
Step | Number of small squares |
1 | 3 |
2 | 6 |
3 | 11 |
4 | a. _____ |
5 | b. _____ |
10 | c. _____ |
12 | d. _____ |
e. _____ |
a. In Step 4, what is the number of small squares?
Step 4 has 18 small squares.
b. In Step 5, what is the number of small squares?
Step 5 has 27 small squares.
c. In Step 10, what is the number of small squares?
Step 10 has 102 small squares.
d. In Step 12, what is the number of small squares?
Step 12 has 146 small squares.
e. In Step , what is the number of small squares?
Compare your answer:
3. Is the number of small squares growing exponentially? Explain how you know.
Compare your answer:
No, from Step 1 to Step 2, the number of squares doubles. From Step 2 to Step 3, the number of squares increases by a factor of . From Step 3 to Step 4, the number of squares increases by a factor of . These growth factors are all different; in contrast, for an exponential function, the values increase by equal growth factors over equal intervals.
The nth expression, , is an example of a quadratic expression. A quadratic expression can be written using a squared term. It can be written in other ways as well, but the expression should be able to be written with the highest exponent on the variable as 2.
- A quadratic relationship is not like a linear relationship because as one quantity increases by a certain amount, the second quantity doesn’t increase by the same amount.
- A quadratic relationship is not like an exponential relationship because as one quantity increases by a certain amount, the second quantity doesn’t change by the same factor. (In this case, if the number of squares grew exponentially, this would mean that, from each step to the next, the number of squares is multiplied by the same factor.)
Are you ready for more?
Extending Your Thinking
Han wrote for the number of small squares in the design at Step in the pattern at the beginning of the activity.
Explain why Han is correct.
Compare your answer:
At Step , there is an by rectangle containing small squares with two columns of squares removed from either side.
On your own, draw and label what Step 3 would look like when Han was writing his expression.
Compare your answer:
I drew a rectangle with three small squares down and five small squares across. Then I removed the two small squares from the first column and the last column.
Video: Quadratic Expressions
Watch the following video to learn more about quadratic expressions.
Self Check
Additional Resources
Writing Expression from Patterns
Find the number of dots in Step 5, and write an expression to find number of dots.
Step 1 - Make a table to help you find the pattern.
Step number | Number of dots |
0 | 4 |
1 | 7 |
2 | 10 |
3 | 13 |
Step 2 - Notice that the start has 2 rows and 2 columns, or 4 dots. Each step adds a row of 2 dots, plus 1 more dot. So, each step adds 3 dots.
Step 3 - Continuing this linear pattern, Step 5 would have 19 dots.
Step 4 - An expression could be . This is a linear expression.
Try it
Try It: Writing Expression from Patterns
Find the number of dots in Step 5, and write an expression to find number of dots.
Here is how to write an expression from a pattern:
Step | Number of dots |
0 | 1 |
1 | 3 |
2 | 9 |
3 | 19 |
Each step has that number of dots squared, then doubled, and then one is added.
So, Step 5 would have 51 dots.
The expression would be , where is the step number.
This is a quadratic expression.