Chapter 5 - Section 5.3 - Special Products - Exercise Set - Page 368: 73

$x^4+2x^2+1$

Using $(a\pm b)^2=a^2\pm2ab+b^2$ or the square of a binomial, the square of the given expression, $\left( x^2+1 \right)^2,$ is \begin{array}{l}\require{cancel} (x^2)^2+2(x^2)(1)+(1)^2 \\\\= x^4+2x^2+1 .\end{array}