因式分解x^3+3x^2y+2xy^2

原式=(x^3+x²y)+(2x²y+2xy²)[将3x²y拆成两项]
=x²(x+y)+2xy(x+y)
=(x+y)(x²+2xy)
=x(x+y)(x+2y)

x^4-3x^3+x^2y+2x^2-2xy=（x^4-3x^3+2x^2）+（x^2y-2xy）
=x^2(x-1)(x-2)+xy(x-2)
=x(x-2)(x^2-x+y)