Ta có : \(4x^4+y^4\)
\(=\left(2x^2\right)^2+\left(y^2\right)^2\)
\(=\left(2x^2\right)^2+4x^2y^2+\left(y^2\right)^2-4x^2y^2\)
\(=\left(2x^2+y^2\right)^2-\left(2xy\right)^2\)
\(=\left(2x^2+y^2-2xy\right)\left(2x^2+y^2+2xy\right)\)
\(4x^2+y^4\)
\(=4x^4+4x^2y^2+y^4-4x^2y^2\)
\(=\left(2x^2+y^2\right)^2-\left(2xy\right)^2\)
\(=\left(2x^2-2xy+y^2\right)\left(2x^2+2xy+y^2\right)\)