Correct. By the Pythagorean Theorem, if c is the length of the diagonal, then $\displaystyle{{c}}^{{2}}={{8}}^{{2}}+{{10}}^{{2}}={64}+{100}={164}\usepackage{cmbright}\Huge\$ . Since $\displaystyle\sqrt{{{{c}}^{{2}}}}=\sqrt{{{164}}},{c}={2}\sqrt{{{41}}}\usepackage{cmbright}\Huge\$ .