Answer
$x^{32}+16x^{30}+120x^{28}$
Work Step by Step
Calculate the first three terms of $(x^2+1)^{16}$ by using Binomial Theorem or Binomial expansion.
This implies
$(x^2+1)^{16}=\displaystyle \binom{16}{0}(x^2)^{16}1^0+\displaystyle \binom{16}{1}(x^2)^{15}1^1+\displaystyle \binom{16}{2}(x^2)^{14}1^2$
or, $=x^{32}+16(x^{30})(1)+120x^{28}$
or, $=x^{32}+16x^{30}+120x^{28}$