## College Algebra (10th Edition)

$x^4-16$
RECALL: $(a-b)(a+b) = a^2-b^2$ Use the formula above with $a=x^2$ and $b=4$ to obtain: $=(x^2)^2-4^2$ Note that $(x^2)^2 = x^{2\cdot2} = x^4$. Thus, the expression above is equivalent to: $=x^4-16$