Common denominator (Please note: the denominators must first be factored!

Got it !

 $\frac{a}{b^2}$ et $\frac{c}{b}$ $\frac{a}{b^2}$ and $\frac{cb}{b^2}$ $\frac{a}{x^2b}$ and $\frac{a}{xb^3}$ $\frac{ab^2}{x^2b^3}$ and $\frac{ax}{x^2b^3}$ $\frac{a-b}{a^2+ab}$ and $\frac{1}{(a+b)^2}$ $\frac{(a-b)}{a(a+b)}$ and $\frac{1}{(a+b)^2}$ so: $\frac{a^2-b^2}{a(a+b)^2}$ and $\frac{a}{a(a+b)^2}$