Find the 4th term in the expansion of (x−2y)12.
Here general term in the expansion of (x−2y)12 is Tr+1=12Cr(x)12−r.(−2y)r =(−1)r 12Cr2r.x12−r.yr Putting r=3, ∴T4=(−1)3 12C3 23 x12−3.y3 =−12C3.8x9y3 =−220×8x9y3=−1760x9y3