1.
1/(x^2+x)=(x^2-x)/[(x^2+x)(x^2-x)]=(x^2-x)/(x^4-x^2)
1/(x^2-x)=(x^2+x)/[(x^2+x)(x^2-x)]=(x^2+x)/(x^4-x^2)
2.
c/ab=c^2/abc
a/bc=a^2/abc
b/ac=b^2/abc