Question

Find the value of k for which the points P(k, -1), Q(2,1) and R(4,5) are collinear.

Answer 1

Given, points P(k, – 1), Q (2, 1) and R(4, 5) are collinear. 

∴ Slope of PQ = Slope of QR .

∴ \(\frac {1-(-1)}{2-k} = \frac {5-1}{4-2}\)

∴ \(\frac {2}{2-k} = \frac {4}{2}\)

∴ 4 = 4 (2 – k) 

∴ 1 = 2 – k 

∴ k = 2 – 1 = 1