I am having trouble understanding why,
$$\frac {xy}{xy^2-x^2y}=\frac{1}{y-x}$$
Why is that the answer and not,
$$\frac{xy}{xy^2-x^2y}=\frac{1}{y^2-x^2}$$
That would have been my answer. Is there something I am missing? I thought you leave the higher degree denominator alone with the numerator if the numerator is of a lower degree than the denominator.
Your fraction can be written as $$\frac{xy}{xy(y-x)}$$ for $$xy\neq 0$$