[JEE Advanced 2000] For $2\le r\le n$, $\binom nr+2\binom n{r-1}+\binom n{r-2}=$
For $2\le r\le n$, $\binom nr+2\binom n{r-1}+\binom n{r-2}=$
(a) $\binom{n+1}{r-1}$
(b) $2\binom{n+1}{r+1}$
(c) $2\binom{n+2}r$
(d) $\binom{n+2}r$
1 Answer
VAVidaara Admin
✓ Vidaara Team
✓ Accepted
· 1mo ago
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Correct answer: (d) $\binom{n+2}r$
Pairing via Pascal's rule twice gives $\binom{n+1}r+\binom{n+1}{r-1}=\binom{n+2}r$.
JEE Advanced 2000 · Binomial Theorem — verified solution by the Vidaara Team.
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