因式分解：x^4+2x^2y^2+9y^4
问题描述：
因式分解：x^4+2x^2y^2+9y^4
答
x^4+2x^2y^2+9y^4
=x^4+6x^2y^2+9y^4-4x^2y^2
=(x^2+3y^2)^2-(2xy)^2
=(x^2+2xy+3y^2)(x^2-2xy+3y^2)