# How do you find the diagonal of a rectangle whose length is 12 in. and whose width is 9 in?

Oct 13, 2015

$15$ in. units

#### Explanation:

The length, width, and diagonal form a right angled triangle, with the diagonal as the hypotenuse.

Hence, Pythagoras Theorem is valid and may used to solve as follows :

${d}^{2} = {12}^{2} + {9}^{2}$

$\therefore d = \sqrt{144 + 81} = 15$

Note we only consider the positive square root since the diagonal is a distance and cannot be negative in this case.