the hmmm cheap way to go about is, usually using the x = 1 and x = 0 pairs.
[tex]y = ab^x\hspace{5em} \begin{array}{|rr|ll} \cline{1-2} x&y\\ \cline{1-2} -2&1\\ -1&3\\ 0&9\\ 1&27\\ 2&81\\ \cline{1-2} \end{array} \\\\[-0.35em] ~\dotfill\\\\ \begin{cases} x=0\\ y=9 \end{cases}\implies 9~~ = ~~ab^0\implies 9=a(1)\implies 9=a~\hfill \underline{y=9b^x} \\\\\\ \begin{cases} x=1\\ y=27 \end{cases}\implies 27~~ = ~~9b^1\implies \cfrac{27}{9}=b^1\implies 3=b~\hfill \underline{y=9(3)^x}[/tex]
