Let be the number of all possible triangles formed by joining vertices of an -sided regular polygon. If , then the value of is
- (A)5✓ Correct
- (B)10
- (C)8
- (D)7
Answer: (A)
Solution
The number of triangles from an -gon's vertices is , and the difference . Setting gives , so , i.e. . Taking the positive root, .
JEE Main · 2013 · 07 Apr 2013 · Offline · Single correct option