Chapter 4 - Polynomials - 4.6 Special Products - 4.6 Exercise Set - Page 277: 57

$t^8+6t^4+9$

Using $(a+b)^2=a^2+2ab+b^2$ or the square of a binomial, the given expression, $ \left( t^4+3 \right)^2 $, is equivalent to \begin{array}{l}\require{cancel} (t^4)^2+2(t^4)\left( 3 \right)+\left( 3 \right)^2 \\\\= t^8+6t^4+9 .\end{array}