Coefficient of \(x^k\) in \((ax+b)^n\) for JEE

Formula

\[\text{If }k=n-r,\text{ then coeff. of }x^k\text{ is }{n\choose r}a^k b^{n-k}={n\choose k}a^k b^{n-k}\]

Variables: \(0\le k\le n\).

Conditions: \(k\) must be an integer.

Finding coefficients of a specified power of \(x\).