Question

Find the slope of line passing through the points (5,9) and (5,-2)

Answer 1

$\sf~m=\dfrac{y_2-y_1}{x_2-x_1}$

(5, 9), (5, -2)
 x1  y1  x2  y2

Plug in what we know:

$\sf~m=\dfrac{-2-9}{5-5}$

Subtract:

$\sf~m=\dfrac{-11}{0}$

We can't divide by zero, so:

$\sf~m=\boxed{\sf~Unde~\!\!\!\!~fined}$