If A = BCD
then
[tex]\begin{gathered} \frac{A}{BC}=\frac{BCD}{BC} \\ \\ D=\text{ }\frac{A}{BC} \end{gathered}[/tex]and
[tex]\begin{gathered} \frac{A}{CD}=\frac{BCD}{CD} \\ B\text{ =}\frac{A}{CD} \end{gathered}[/tex]and
[tex]\begin{gathered} \frac{A}{BD}=\frac{BCD}{BD} \\ C=\frac{A}{BD} \end{gathered}[/tex]