Question

What is the slope of the line that passes through the points (3, 4) and (5, –4)?

Answer 1

Call one point \((x_1,y_1)\) and the other point \((x_2,y_2)\). I usually use \((x_1,y_1)\) for the point to the left.
The slope is then \[m = \frac{y_2-y_1}{x_2-x_1}\]