Let T n be the number of all possible triangles formed by joining vertices of an n -sided regular polygon. If T n + 1 - T n = 10 , then the value of n is :

Step-by-step solution

Number of triangles = C 3 n Given: C 3 n + 1 - C 3 n = 10 ⇒ n 2 - n - 20 = 0 ⇒ n - 5 n + 4 = 0 ⇒ n = 5 ,     ∵ n ≠ 0