Mathematics · important
Product identity for combinations for JEE
Permutations and combinations
Formula
\(\,{}^nC_r\,{}^rC_k={}^nC_k\,{}^{n-k}C_{r-k}\)
Variables: \(n,r,k\) are integers.
Conditions: \(0\le k\le r\le n\).
Two-stage selection and combinatorial simplification.