How does [{9x^(2)}/(1+x^(4)y^(2)) -2xy] become [{9x^(2)(1+x^(4)y^(2)) -xy}/(1+x^(4)y^(2)) ] ? I don't understand how (1+x^(4)y^(2)) got up onto the numarator.

Answer 1

It's easier to read without all the extra ()[]{}...
Secondly, the two expressions are in no way equal.

9x^2/(1+x^4y^2) - 2xy = (9x^2 - 2xy(1+x^4y^2))/(1+x^4y^2)