Factoring help...?

Question

I need some help with the following problem:

x^2 + 4xy - 21y^2

Thanks in advance.

Answer 1

ok. we want to find factors of -21 that add up to + 4.

so, list the factors of -21
(-1,21) (-7,3) (-3,7) (1,21)

we see that -3 + 7 = 4

so, you can factor this as

(x - 3y)(x + 7y)

Answer 2

[(x+2)(y+2)]^2