A(1,6), B(-4,9) and C(9,9), D(3,1) are the lines through the points perpendicular

Question

A(1,6), B(-4,9) and C(9,9), D(3,1) are the lines through the points perpendicular?

Answer 1

In fact, lines through AC and BD, and AD and BC are not perpendicular either.

Answer 2

Find slopes of both lines. If product of the slopes is -1 then the line are perpendicular.

 

Slope of line AB = (9-6)/(-4 -1) = -3/5

 

Slope of line CD = (1-9)/(3-9) = 8/6=4/3

 

Products of two slopes is not -1 so lines are not perpendicular

:)