The coefficient of x4 in the expansion of  x2−3x210 , is

Suppose x4 occurs in  (r + 1)th term. we have , Tr+1=10Crx210−r−3x2r=10Crx10−3r(−3)r2r−10This will contain x4 , if ∴ 10−3r=4⇒3r=6⇒r=2So,  x4occurs in 3rd term and its coefficient is  10C2×(−3)2×22−10=10C2×3228=5×9×3228=405256