Let T<sub>n</sub> denote the number of triangles which can be formed by using the vertices of a regular polygon of n sides. If T<sub>n+1</sub> - T<sub>n</sub> = 21, then n equals:
According to the question we have \[ {}^{n+1}C_3 - {}^nC_3 = 21 \] We know \[ {}^8C_3 - {}^7C_3 = 21 \Rightarrow n = 7 \]
Reinforce your conceptual grasp with related questions from MAH MCA CET 2013:
Take timed full-length mock tests with authentic question distributions, negative marking (+12/-3 in Math), and instant All India Rank calculation.
Start Free Mock Test Series →