Chapter 4 - Quadratic Functions and Equations - 4-4 Factoring Quadratic Expressions - Practice and Problem-Solving Exercises - Page 222: 84

$100(9x+10)(9x-10)$

Factoring the $GCF= 100 ,$ the given expression, $ 8100x^2-10000 ,$ is equivalent to \begin{align*} 100(81x^2-100) .\end{align*} Using the factoring of the difference of $2$ squares which is given by $a^2-b^2=(a+b)(a-b),$ the expression above is equivalent to \begin{align*} & 100[(9x)^2-(10)^2] \\&= 100[(9x+10)(9x-10)] \\&= 100(9x+10)(9x-10) .\end{align*}