find the coefficient of x^n in the expansion of (1+x)(1-x)^n

Expand the (1-x)ⁿto get the coeff. of xⁿandx^n-1. These terms when multiplied with the bracket term (1+x) will give all the terms having xⁿ. The sum of coefficients of both these terms will be the coeff. of xⁿin this expansion.