Confronto tra frazioni

Date le frazioni $\displaystyle \frac{a}{b}$ e $\displaystyle \frac{c}{d}$: $\displaystyle \frac{a}{b}<\frac{c}{d}$, se $a\cdot d < b\cdot c$; $\displaystyle \frac{a}{b}>\frac{c}{d}$, se $a\cdot…