初一数学题与代数式有关
问题描述：
初一数学题与代数式有关
化简
（a+b)(a^2-3ab=9b^2)-(a-3b)(a^2+3ab+9b^2)
（x+y)^2(y+z-x)(z+x-y)+(x-y)^2(x+y+z)(x+y-z)
已知z^2=x^2+y^2,化简（x+y+z)(x-y+z)(-x+y+z)(x+y-z)
已知x(x-1)-(x^2-y)=-2
求x^2+y^2/2-xy
不需要完整的过程有2步到3步过程就可以了
答
2.
（x+y)^2(y+z-x)(z+x-y)+(x-y)^2(x+y+z)(x+y-z)
=（x+y)^2[z-(x-y)](z+x-y)+(x-y)^2[(x+y)^2-z^2]
=（x+y)^2z^2(x^2-y^2)^2+(x^2-y^2)^2-(x-y)^2z^2
=4xyz^2