Gradient = m = y2−y1x2−x1\frac{y_2 - y_1}{x_2 - x_1}x2−x1y2−y1
= −2−12+1\frac{-2 - 1}{2 + 1}2+1−2−1
= −33\frac{-3}{3}3−3
= -1
