可以用平方差公式
原式
=[2(x+y)]^2-(x-y)^2
=[(2x+2y)-(x+y)][(2x+2y)+(x-y)]
=(x+3y)(3x+y)
或者直接展开括号
原式
=3x^2+10xy+3y^2
=(3x^2+9xy)+(xy+3y^2)
=3x(x+3y)+y(x+3y)
=(3x+y)(x+3y)
可以用平方差公式
原式
=[2(x+y)]^2-(x-y)^2
=[(2x+2y)-(x+y)][(2x+2y)+(x-y)]
=(x+3y)(3x+y)
或者直接展开括号
原式
=3x^2+10xy+3y^2
=(3x^2+9xy)+(xy+3y^2)
=3x(x+3y)+y(x+3y)
=(3x+y)(x+3y)