### Key Terms

- break-even point
- The point at which the revenue equals the costs is the break-even point; $C\left(x\right)=R\left(x\right).$

- coincident lines
- Coincident lines have the same slope and same
*y*-intercept.

- complementary angles
- Two angles are complementary if the sum of the measures of their angles is 90 degrees.

- consistent and inconsistent systems
- Consistent system of equations is a system of equations with at least one solution; inconsistent system of equations is a system of equations with no solution.

- cost function
- The cost function is the cost to manufacture each unit times $x$, the number of units manufactured, plus the fixed costs;
*C*(*x*) = (cost per unit)*x*+ fixed costs.

- determinant
- Each square matrix has a real number associated with it called its determinant.

- matrix
- A matrix is a rectangular array of numbers arranged in rows and columns.

- minor of an entry in a $3\phantom{\rule{0.2em}{0ex}}\xc3\u2014\phantom{\rule{0.2em}{0ex}}3$ determinant
- The minor of an entry in a $3\phantom{\rule{0.2em}{0ex}}\xc3\u2014\phantom{\rule{0.2em}{0ex}}3$ determinant is the $2\phantom{\rule{0.2em}{0ex}}\xc3\u2014\phantom{\rule{0.2em}{0ex}}2$ determinant found by eliminating the row and column in the $3\phantom{\rule{0.2em}{0ex}}\xc3\u2014\phantom{\rule{0.2em}{0ex}}3$ determinant that contains the entry.

- revenue
- The revenue is the selling price of each unit times
*x*, the number of units sold;*R(x*) = (selling price per unit)*x*.

- row-echelon form
- A matrix is in row-echelon form when to the left of the vertical line, each entry on the diagonal is a 1 and all entries below the diagonal are zeros.

- solutions of a system of equations
- Solutions of a system of equations are the values of the variables that make
*all*the equations true; solution is represented by an ordered pair $\left(x,y\right).$

- solutions of a system of linear equations with three variables
- The solutions of a system of equations are the values of the variables that make all the equations true; a solution is represented by an ordered triple $\left(x,y,z\right).$

- square matrix
- A square matrix is a matrix with the same number of rows and columns.

- supplementary angles
- Two angles are supplementary if the sum of the measures of their angles is 180 degrees.

- system of linear equations
- When two or more linear equations are grouped together, they form a system of linear equations.

- system of linear inequalities
- Two or more linear inequalities grouped together form a system of linear inequalities.