Answer
$(x-7)^2$
Work Step by Step
RECALL:
$a^2-2ab+b^2=(a-b)^2$
The given trinomial can be written as:
$=x^2-2(x)(7) + 7^2$
This trinomial is in the same form as the perfect square trinomial above, where $a=x$ and $b=7$.
Factor the perfect square trinomial using the formula above to obtain:
$=(x-7)^2$