JEE PYQ

[JEE Advanced 2001] t n binom n3 is the number of triangles from a regular n gon

VAVidaara Admin Asked 2d ago 0 views 1 answer
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$T_n=\binom n3$ is the number of triangles from a regular $n$-gon. If $T_{n+1}-T_n=21$, then $n$ equals

(a) $5$
(b) $7$
(c) $6$
(d) $4$

1 Answer

VAVidaara Admin ✓ Vidaara Team ✓ Accepted · 2d ago ▲ 0

Correct answer: (b) $7$

$T_{n+1}-T_n=\binom n2=21\Rightarrow n(n-1)=42\Rightarrow n=7$.

JEE Advanced 2001 · Permutations and Combinations — verified solution by the Vidaara Team.

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