Chapter 9.1, Problem 48E

It can be shown that the length of a diagonal of a right rectangular prism with dimensions $l$, $w$, and $h$ is given by $d=\sqrt{l^2+w^2+h^2}$. Use this formula to find the length of the diagonal when $l=12 in.$, $w=4 in$., and $h=3 in$.