Answer
$f(-x)=a^{-x}=\dfrac{1}{a^x}=\dfrac{1}{f(x)}$
Work Step by Step
Given ,
$f(x)=a^{x}$...........$(1)$
Then,
$f(-x)= a^{-x}$...........[from (1)]
$f(-x)= \frac{1}{a^{x}}$........[by laws of exponents]
$f(-x)= \frac{1}{f(x)}$ ..........[by using (1)]
Hence Proved.
