(x+y)^-3分之（2a）^-1
=2a分之(x+y)^3
x^2(x-1)^-1-[1+（x^2-x)^-1]
=x^2/(x-1)-[1+1/(x^2-x)]
=x^3/x(x-1)-x(x-1)/x(x-1)-1/x(x-1)
=(x^3-x^2+x-1)/x(x-1)
=(x-1)(x^2-1)/x(x-1)
=(x^2-1)/x
7^-1(x+y)(x-y)^-2
=1/7*(x+y)/(x-y)^2
=(x+y)/[7(x-y)^2]
注意
/是分数线
是分子/分母
即1/2是2分子1