x立方+3x平方-4x-12 x平方+2x-6y-9y平方 分解因式

x^3+3x^2-4x-12
=(x^3-4x)+(3x^2-12)
=x(x^2-4)+3(x^2-4)
=(x^2-4)(x+3)
=(x-2)(x+2)(x+3)
x^2+2x-6y-9y^2
=(x^2+2x+1)-(9y^2+6y+1)
=(x+1)^2-(3y+1)^2
=[(x+1)+(3y+1)]*[(x+1)-(3y+1)]
=(x+3y+2)(x-3y)