Algebra and Trigonometry 10th Edition

Slope of Line 1 : $m_1=\frac{y_2-y_1}{x_2-x_1}=\frac{2-8}{-4-4}=\frac{-6}{-8}=3/4$ Slope of Line 1 : $m_2=\frac{y_2-y_1}{x_2-x_1}=\frac{-5-(\frac{1}{3})}{3-(-1)}=\frac{\frac{-16}{3}}{4}=-4/3$ Hence the lines are perpendicular as $m_1 * m_2 = -1$