[tex]\sqrt{3p^2+6}-9=0\implies \sqrt{3p^2+6}=9\implies \stackrel{\textit{squaring both sides}}{(\sqrt{3p^2+6})^2=9^2} \\\\\\ \sqrt{(3p^2+6)^2}=81\implies 3p^2+6=81\implies 3p^2=75 \\\\\\ p^2=\cfrac{75}{3}\implies p^2=25\implies p=\pm\sqrt{25}\implies p=\pm 5\implies \stackrel{positive}{p=5}[/tex]
