# How do you solve 15e^-x=645?

Jan 16, 2017

$x \cong - 3.76$

#### Explanation:

${e}^{-} x = \frac{645}{15} = 43$

We take logs of both sides:

$\log {e}^{-} x = \log 43 \cong 3.76$

But $\log {e}^{-} x$, by definition, is the power to which we raise the base $e$ to get ${e}^{-} x$, so here $- x \cong 3.76$.

And $x \cong - 3.76$