81+3x^3 因式分解

题目

81+3x^3 因式分解
y^4-8y x^5-(x^2)(y^3) 急
好像是按照a^3+b^3=(a+b)(a^2-ab+b^2),算的,

答案

81+3x^3
=3(x^3+3^3)
=3(x+3)(x^2-3x+9)
y^4-8y
=y(y^3-2^2)
=y(y-2)(y^2+2y+4)
x^5-(x^2)(y^3)
=x^2(x^3-y^3)
=x^2(x-y)(x^2+xy+y^2)