Answer
(a) $81$, $(4,81)$.
(b) $-2$, $(-2,\frac{1}{9})$.
Work Step by Step
(a) Given $f(x)=3^x$, we have $f(4)=3^4=81$ which gives a point $(4,81)$.
(b) For $f(x)=\frac{1}{9}=3^{-2}$, we have $3^x=3^{-2}$, which gives $x=-2$ and a point $(-2,\frac{1}{9})$.
