## Algebra: A Combined Approach (4th Edition)

As $\frac{a}{b}$ = $\frac{c}{d}$, they are proportional to each other, we can multiply both sides by the LCD, $bd$, resulting in $ad = bc$. $ad$ and $bc$ are known as the $\underline{cross \space products}$ of the proportion and they are equal to each other.