arunspanda wrote:
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
A. 5
B. 6
C. 7
D. 8
E.10
In a plane if there are n points of which no three are collinear, then the number of triangles that can be formed by joining them isC^3_n .
We are given thatT_{n+1} - T_n =C^3_{n+1}-C^3_n= 10 --> C^3_{n+1}-C^3_n=\frac{(n+1)!}{3!(n-2)!}-\frac{n!}{3!(n-3)!} =10
...