Answer
$(x-6y)(x+2y)$
Work Step by Step
To factor a trinomial in the form $x^2+bx+c$, we must find two numbers whose product is $c$ and whose sum is $b$. We then insert these two numbers into the blanks of the factors $(x+\_)(x+\_)$.
In the case of $x^2-4xy-12y^2$, we are looking for two numbers whose product is $-12y^2$ and whose sum is $-4y$. The numbers $-6y$ and $2y$ meet these criteria, because $$-6y\times2y=-12y^2\;\text{and}\;-6y+2y=-4y$$When we insert these numbers into the blanks, we arrive at the factors $(x-6y)(x+2y)$.
