Answer
$(5y-1)^2$
Work Step by Step
RECALL:
$a^2-2ab+b^2=(a-b)^2$
The given trinomial can be written as:
$=(5y)^2-2(5y)(1) + 1^2$
This trinomial is in the same form as the perfect square trinomial above, where $a=5y$ and $b=1$.
Factor the perfect square trinomial using the formula above to obtain:
$=(5y-1)^2$