## Elementary Technical Mathematics

$$(cd+4)(cd-4)$$
$c^{2}d^{2}-16$ This is the difference between two squares. There is a simple formula for this case: $x^{2}-y^{2}=(x+y)(x-y)$ So, applying this formula: We need to take the square of both terms. $\sqrt (c^{2}d^{2})=cd$ $\sqrt 16=4$ So the answer would look like: $$(cd+4)(cd-4)$$ (One with a positive sign and one with a negative sign.)