In the expansion of x3−1x2n,n∈N, if the sum of the coefficients of x5 and x10is 0, then n is

x3−1r2nGeneral term Tr+1=n!r!(n−r)!(−1)n−rx5n−2nIf 5r−2n=5, then 5r=2n+5 or r=2n5+1If 5r−2n=10, then 5r=2n+10 or r=2n5+2x5 and x10 terms occurs if n=5kGiven that sum of x5 and x10 is zero.⇒5k!(2k+1)!(3k−1)!−5k!(2k+2)!(3k−2)!=0or  13k−1−12k+2=0or   k=3⇒n=15