In the expansion of x3−1x215, the constant term, is

Let (r+1)th  term be the constant term in the  expansion of x3−1x215∴ Tr+1=15Crx315−r−1x2r  is independent of x⇒Tr+1=15Crx45−5r(−1)r is independent of x ⇒45−5r=0⇒r=9 Thus, tenth term is independent of x and is given byT10=15C9(−1)9=−15C9