(x+2)(x+3)+x^2-5x-8 x^3-x^2y-xy^2+y^3 18x^2-21xy+5y^2因式分解（写出过程）

题目

(x+2)(x+3)+x^2-5x-8 x^3-x^2y-xy^2+y^3 18x^2-21xy+5y^2因式分解（写出过程）
第一题到8
第二题到y＾3
第三题到最后

答案

(x+2)(x+3)+x^2-5x-8
=x^2+5x+6+x^2-5x-8
=2x^2-2
=2(x^2-1)
=2(x+1)(x-1);
x^3-x^2y-xy^2+y^3
=(x^3-x^2y)-(xy^2-y^3)
=x^2*(x-y)-y^2*(x-y)
=(x-y)(x^2-y^2)
=(x-y)(x-y)(x+y)
=(x+y)(x-y)^2;
18x^2-21xy+5y^2
=(3x-y)(6x-5y).