Let be the number of all possible triangles formed by joining vertices of an -sided…

MATHEMATICS · Single correct · AoPS · Mathematics · Follow the Rules · Follow the Rules

Problem

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

, the value of

n

is (1) 5 (2) 10 (3) 8 (4) 7