Thinking Mathematically (6th Edition)

slope = $0$ The line that passes through the given points is horizontal.
RECALL: (1) The slope $m$ of a line can be found using the formula $m=\dfrac{y_2-y_1}{x_2-x_1}$. (2) A line with a positive slope means the line rises from left to right. A negative slope means the line falls from left to right. (3) A zero slope means the line is horizontal. An undefined slope means the line is vertical. Solve for the slope using the formula in (1) to obtain: $m=\dfrac{1-1}{-2-5}=\dfrac{0}{-7}=0$ The slope is zero, so the line is horizontal.