【因式分解】计算 化简或求值

1.(x^2-y^2)(x^2+xy+y^2) / (x+y)(x^3-y^3)
=（x+y）(x-y)(x²+xy+y²)/(x+y)(x-y)(x²+y²+xy)
=1;
2.(x^2-4x+4)(3-x) / (2x-6)(x^2+x-6)
=(x-2)²(3-x)/2(x-3)(x+3)(x-2)
=-(x-2)/2(x+3);
3.已知 x+y=1,xy= -2,求(x^2+y^2+xy) / (x^2+y^2-xy) 的值
x²+y²=(x+y)²-2xy=1+4=5;
原式=(5-2)/(5+2)=3/7;
4.已知（x^2+y^2）（x^2+y^2-1）=12,求x^2+y^2的值
（x²+y²）²-(x²+y²)-12=0;
(x²+y²-4)(x²+y²+3)=0;
x²+y²=4或x²+y²=-3;再问几题哦。1. 3a^2-6ab+3b^2-5a+562.25a^2-9b^2+10a+13. x^2y^2-5x^2y-6x^21. 3a^2-6ab+3b^2-5a+5b=3(a-b)²-5(a-b)=(a-b)(3a-3b-5)第一问是-5a+5b吧，是56不好解2.25a^2-9b^2+10a+1=(5a+1)²-9b²=(5a+1+3b)(5a+1-3b);3. x^2y^2-5x^2y-6x^2=x²(y²-5y-6)=x²(y-6)(y+1)不懂请追问，请采纳，谢谢！