Points P ≡ (-1,1), Q ≡ (1,-4), R ≡ (6,-2) are given. Find the gradients of the lines PQ and QR, and show that they are perpendicular.
Here's what I've got - is this correct?
slope of PQ = (y2 - y1) /(x2 -x1) = (-4 -1)/(1 - (-1)) = -5/2
slope of QR = ( -2 - (-4) ) / (6 - 1) = 2/5
slope of PQ * slope of Qr = -5/2 * 2/5 = -1
so PQ perpendicular to QR