222. $\log x=3 \log a+2 \log (a+b)-\frac{1}{2} \log c$.
Solution. According to the converse theorems $3,4,1$ and 2, we obtain

$$
\begin{gathered}
\log x=\log a^{3}+\log (a+b)^{2}-\log \sqrt{\bar{c}}=\log \frac{a^{3}(a+b)^{2}}{\sqrt{\bar{c}}} ; \log x=\log \frac{a^{3}(a+b)}{\sqrt{\bar{c}}} ; \\
x=\frac{a^{3}(a+b)}{\sqrt{c}} .
\end{gathered}
$$