Answer
$(x+5+3y)(x+5-3y)$
Work Step by Step
Separate the terms into two groups. Factor the first group by trial and error. Then use the formula $a^2-b^2=(a+b)(a-b)$ to factor further.
$x^2+10x+25-9y^2$
$(x^2+10x+25)-9y^2$
$(x+5)(x+5)-9y^2$
$(x+5)^2-9y^2$
$(x+5+3y)(x+5-3y)$
