From George F. Simmons 'Precalculus' book, Algebra section, 5(d); Combine and Simplify
$$\frac{x}{xy^2} + \frac{y}{x^2y}$$
Combine: = $$\frac{x(x^2y) + y(xy^2)}{(xy^2)(x^2y)}$$ Simplify: = $$\frac{x(x^2y) + y(xy^2)}{xy(x^2y^2)}$$
The given answer, which I can't figure out how he arrives at it is: $$\frac{x^2 +y^2}{x^2y^2}$$
$$\frac{x}{xy^2}+\frac{y}{x^2y}=\frac{x}{x}\cdot\frac{x}{xy^2}+\frac{y}{y}\cdot\frac{y}{x^2y}=\frac{x\cdot x}{xy^2\cdot x}+\frac{y\cdot y}{x^2y\cdot y}=\frac{x^2}{x^2y^2}+\frac{y^2}{x^2y^2}=\frac{x^2+y^2}{x^2y^2}$$