Mathematics · important
Useful permutation recurrence 2 for JEE
Meaning of P(n,r) and C(n,r)
Formula
\(\,{}^nP_r=(n-r+1)\,{}^nP_{r-1}\)
Variables: \(n,r\) are integers.
Conditions: \(1\le r\le n\).
Building permutations stepwise and evaluating ratios.