## Elementary and Intermediate Algebra: Concepts & Applications (6th Edition)

$x\in\{-1,4\}$
On the LHS, apply $a^{m}\cdot a^{n}=a^{m+n}.$ On the RHS, recognize $81$ as $3^{4}$ $3^{3x+x^{2}}=3^{4}\qquad$ ... apply the exponential equality principle $3x+x^{2}=4$ $x^{2}+3x-4=0$ $(x+1)(x-4)=0$ $x=-1, x=4$