Answer
$f(x)=2^x$
Work Step by Step
First, we have to find the function, by calculating the constant, $a$.
If the function contains this point (3,8), then $f(3)=8$, this means:
$a^3=8$
We take the cube root of both sides :
$a=2$
Therefore, with $a=2$ the function is: $f(x)=2^x$.