Give a rule of the $to\pi mf\left(x\right)=a^{x}$ to define the exponential function whose graph contains the given point.
(a) $\left(2,16\right)$
(b) $\left(-6.64\right)$
$\left(a\right)$ The graph of the exponential function $f\left(x\right)=4^{x}$ passes through the point $\left(2,16\right)$
(Simplify your answer. Use integers or fractions for any numbers in the expression.)
$\left(b\right)$ The graph of the exponential function $f\left(x\right)=\bar{1} $ pases through the point $\left(-6.64\right)$
(Simplify $y0∪r$ answer. Use integers or fractions for any numbers in the expression.)