Answer
$ \displaystyle \log_{5/4}\left(\frac{16}{25}\right)=-2$
Work Step by Step
From the definition of logarithms,
for $a>0$, $a\neq 1$, and $x > 0$,
$y=\log_{a}x$ means $a^{y}=x$.
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$\left(\displaystyle \frac{5}{4}\right)^{-2}=\frac{16}{25}\quad$ means $\displaystyle \quad \log_{5/4}\left(\frac{16}{25}\right)=-2$
