Precalculus (6th Edition) Blitzer

$y=2.5e^{x\ln 0.7}$, $y=2.5e^{-0.357x}$
$y=ab^{x}$ is equivalent to $y=ae^{x\ln b}$ $y=2.5(0.7)^{x}$ is equivalent to $y=2.5e^{x\ln 0.7}$ With $\ln 0.7\approx-0.357,$ $y=2.5e^{-0.357x}$