Precalculus (6th Edition) Blitzer

$8$
RECALL $y=\log{x} \longleftrightarrow 10^y=x.$ Let $y=\log{10^8}.$ Use the definition above to obtain $y=\log{10^8} \longrightarrow 10^y=10^8.$ Use the rule "if $a^x=a^y$, then $x=y$" to obtain $y=8.$ Therefore, $\log{10^8} = 8.$