## Precalculus (10th Edition)

$-a$
We know that $\log_a {x}-\log_a {y}=\log_a {\left(\frac{x}{y}\right)}$. Hence,, $\ln {0.5}=\ln{\frac{1}{2}}=\ln{1}-\ln{2}$ Note that $\ln {1}=0$. Thus, $\ln{1}-\ln{2} \\=0-\ln{2} \\=0-a \\=-a$