Answer
$f(-2)=\frac{1}{49}$
Work Step by Step
The given function is
$\Rightarrow f(x)=7^x$
Substitute $-2$ for $x$.
$\Rightarrow f(-2)=7^{-2}$
Use $a^{-n}=\frac{1}{a^n}$.
$\Rightarrow f(-2)=\frac{1}{7^{2}}$
Use $7^2=49$.
$\Rightarrow f(-2)=\frac{1}{49}$