# How do you factor -x^2y^2 + x^4 + 4y^2 - 4x^2 ?

Feb 2, 2016

Combination

#### Explanation:

We have the equation as

$f \left(x , y\right) = - {x}^{2} {y}^{2} + {x}^{4} + 4 {y}^{2} - 4 {x}^{2}$
$= {x}^{4} - {x}^{2} {y}^{2} - 4 {x}^{2} + 4 {y}^{2}$
$= {x}^{2} \left({x}^{2} - {y}^{2}\right) - 4 \left({x}^{2} - {y}^{2}\right)$
$= \left({x}^{2} - {y}^{2}\right) \setminus \times \left({x}^{2} - 4\right)$