If the rth  term in the expansion of (x3−2x2)10  contains x4  then r  equal to

Given expansion is (x3−2x2)10   We have general term in the expansion (x+a)n (∴  Tr+1= nCr xn−r (a)r  be the expansion of (x+a)n)   rth term in the expansion Tr=Tr−1+1= 10Cr−1 (x3)11−r (−2x2)r−1 Tr= 10Cr−1(−2)r−1311−rx13−  3r (∴xaxb=xa−b) Here x13−  3r compare with x4 then we get ⇒x13−  3r=x4 This constrains x4  if 13−3r=4  ∵r=3