To solve the equation \(\log (a+b) = \log (ab)\), we can use the property of logarithms that states if \(\log(x) = \log(y)\), then \(x = y\). Therefore, we can set the arguments of the logarithms equal to each other: \(a + b = ab\). We can then rearrange this equation to solve for one of the variables in terms of the other.
Step 1: Set Up the Equation
We start with the equation derived from the logarithmic property:
\[
\log(a + b) = \log(ab) \implies a + b = ab
\]
Step 2: Rearrange the Equation
Rearranging the equation gives us:
\[
ab - a - b = 0
\]
This can be rewritten as:
\[
a + b - ab = 0
\]
Step 3: Solve for \(a\)
To solve for \(a\) in terms of \(b\), we can rearrange the equation:
\[
a = \frac{b}{b - 1}
\]
Final Answer
Thus, the solution for \(a\) in terms of \(b\) is:
\[
\boxed{a = \frac{b}{b - 1}}
\]