Show that the following points are collinear:
A(5, 1), B(1, –1) and C(11, 4)
To show that the points are collinear, we show that the area of triangle is equilateral = 0
Δ = 0
Δ = 1/2{x1(y2−y3) + x2(y3−y1) + x3(y1−y2)}
⇒ Δ = 1/2{5(–1– 4) + 1 (4– 1) + 11 (1 + 1)}
⇒ 1/2{–25 + 3 + 22}
= 0
Hence collinear