Chapter 4 - Polynomials - 4.6 Special Products - 4.6 Exercise Set - Page 276: 25

$1-25t^6$

Using $(a+b)(a-b)=a^2-b^2$ or the product of the sum and difference of like terms, the given expression, $ (1-5t^3)(1+5t^3) $, is equivalent to \begin{array}{l}\require{cancel} (1)^2-(5t^3)^2 \\\\= 1-25t^6 .\end{array}