amp;(1+x)(1−x2)(1+x3+x23+x31)5amp;=(1+x)(1−x2)((1+x1)3)5amp;=x15(1+x)2(1−x)(1+x)15amp;=x15(1+x)17−x(1+x)17
=coeff(x3) in the expansion ≈coeff(x18) in
amp;(1+x)17−x(1+x)17amp;=0−1amp;=−1
coeff(x−13) in the expansion ≈coeff(x2) in
amp;(1+x)17−x(1+x)17amp;=(172)−(171)amp;=17×8−17amp;=17×7amp;=119
Hence Answer =119−1=118