a(x-y)分之x,b(y-x)分之y
公分母ab(x-y)
所以x/a(x-y)=bx/ab(x-y)
y/b(y-x)=-ay/ab(x-y)
(2-x)的平方分之1,(x+2)(x-2)分之x
(2-x)²=(x-2)²
所以公分母(x-2)²(x+2)
所以1/(2-x)²=(x+2)/(x-2)²(x+2)
x/(x+2)(x-2)=(x²-2x)/(x-2)²(x+2)
计算：(x的平方-4x+3分之x的平方-4）的平方乘（x的平方+3x+2分之x-3)除以（-x的平方-1分之x-2)
=[(x+2)(x-2)/(x-1)(x-3)]²*[(x-3)/(x+1)(x+2)]*(-x²-1)/(x-2)
=(-x²-1)(x+2)²(x-2)²(x-3)/[(x-1)²(x-3)²(x+1)(x+2)(x-2)]
=(-x²-1)(x+2)(x-2)/[(x-1)²(x-3)(x+1)]
化简a+2分之a的平方-4除以（a-2)乘以a-2分之1
=[(a+2)(a-2)/(a+2)]÷(a-2)*1/(a-2)
=(a-2)/(a-2)²
=1/(a-2)