The sum of the coefficients of x32 and x−17 in(x4−1x3)15  is

Given expansion (x4−1x3)15 isWe have general term in the expansion (x+a)n(∴  Tr+1= nCr xn−r (a)r be the expansion of (x+a)n)Tr+1=15Cr(x4)15−r(−1x3)rTr+1=15Cr(x)60−7r(−1)r(x)60−7r  compare with x32⇒x60−7r=x3260−7r=32⇒r=4⇒x60−7r=x−1760−7r=−17⇒r=11The sum of the coefficients of x32 and x−17 is=15C4+15C11(−1)11(∴15C4=15C11)                                                                                 ⇒15C4−15C11=0