Chapter 5 - Section 5.3 - Special Products - Exercise Set - Page 368: 61

$x^{16}+6x^8+9$

Using $(a\pm b)^2=a^2\pm2ab+b^2$ or the square of a binomial, the square of the given expression, $\left( x^8+3 \right)^2,$ is \begin{array}{l}\require{cancel} (x^8)^2+2(x^8)(3)+(3)^2 \\\\= x^{16}+6x^8+9 .\end{array}