Question

Evaluate f(-3) for f(x)=2^x

Answer 1

$f(-3)=2^{-3}=\dfrac{1}{8}$

Answer 2

to the risk of sounding redundant.

$\bf ~~~~~~~~~~~~\textit{negative exponents} \\\\ a^{-n} \implies \cfrac{1}{a^n} \qquad \qquad \cfrac{1}{a^n}\implies a^{-n} \qquad \qquad a^n\implies \cfrac{1}{a^{-n}} \\\\ -------------------------------\\\\ f(-3)=2^{-3}\implies f(-3)=\cfrac{1}{2^3}\implies f(-3)=\cfrac{1}{8}$