Question

Find the number of triangles formed by joining 12 points if four points are collinear

Answer 1

There are 12 points on the plane

When 4 of these points are collinear

∴ Number of triangles that can be obtained from these points = ¹²C₃ – ⁴C₃

= `220 - (4!)/(3! xx 1!)`

= `220 - (4 xx 3!)/(3!)`

= 220 – 4

= 216