## Precalculus (6th Edition) Blitzer

$(x-7)^2$
RECALL: A perfect square trinomial can be factored using either of the following formulas. (i) $a^2+2ab+b^2=(a+b)^2.$ (i) $a^2-2ab+b^2=(a-b)^2.$ The given perfect square trinomial can be written as $x^2-2(x)(7)+7^2.$ Factor using formula (ii) above with $a=x$ and $b=7$ to obtain $(x-7)^2.$