Answer
-2.8074
Work Step by Step
For all positive numbers $a$, where $a\ne1$, and all positive numbers $x$, we know that $y=log_{a}x$ means the same as $x=a^{y}$.
Therefore, $log_{2}(\frac{1}{7})=x$ means the same as $2^{x}=\frac{1}{7}$.
By using a calculator to approximate, we know that $x=-2.8074$, because $2^{-2.8074}=\frac{1}{7}$.