we know the triangle is an isosceles, so it has twin sides, and then the hypotenuse, since it's a right-triangle, we can just use the pythagorean theorem for that.
[tex]\bf \textit{using the pythagorean theorem} \\\\ c^2=a^2+b^2\implies c=\sqrt{a^2+b^2} \qquad \begin{cases} c=hypotenuse\\ a=\stackrel{adjacent}{3\sqrt{2}}\\ b=\stackrel{opposite}{3\sqrt{2}}\\ \end{cases} \\\\\\ c=\sqrt{(3\sqrt{2})^2+(3\sqrt{2})^2}\implies c=\sqrt{(3^2\cdot 2)+(3^2\cdot 2)}\implies c=\sqrt{18+18} \\\\\\ c=\sqrt{36}\implies c=6[/tex]
