The term contacting x3  in the expansion of (x−2y)7  is

Given  expansion is  (x−2y)7   We 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= 7Crx7−r(−2y)r  x7−r  compare with x3  then⇒x7−r=x3 Contains x3  it 7−r=3   ∵r=4 . So T5 is the required term.