Suppose $f(x)$ gives the amount of a radioactive isotope with a half life of 5 years, after x years. $f(x)$ is a function of the form $$f(x) = a^{bx}$$ for some constants $a$ and $b$.
Then $f(x) =$ .
Hint: The choice of $a$ and $b$ are not unique, but the function is, and WeBWorK will accept any correct choice of $a$ and $b$. Just look for a half life of $5$.