Tell what can be done to both sides of the equation
$$
a d=b c
$$
to get each of the following equations.
$$\text { Example: } \frac{a}{b}=\frac{c}{d}$$
$$
\begin{array}\text{Answer: Divide} \text{ by } { bd } \\
\frac{a d}{b d}=\frac{b c}{b d}, \text { and so } \frac{a}{b}=\frac{c}{d}
\end{array}
$$
$$\frac{d}{c}=\frac{b}{a}$$