## Geometry: Common Core (15th Edition)

$m = 0$
We are given the two points X $(-a, b)$ and Y $(a, b)$. Let's use the formula to find the slope $m$ given two points: $m = \frac{y_2 - y_1}{x_2 - x_1}$, where $(x_1, y_1)$ and $(x_2, y_2)$ are points on the line. Let's plug in the values into this formula: $m = \frac{b - b}{a - (-a)}$ Simplify the numerator and denominator: $m = \frac{0}{2a}$ Simplify the fraction to solve: $m = 0$