# The length and width of a rectangle are 15 cm and 8 cm respectively. How do you find the length of a diagonal?

Oct 14, 2015

$17 c m$

#### Explanation:

The length, width and diagonal of the rectangle form a right-angled triangle, with the diagonal as the hypotenuse, so Pythagoras Theorem is valid to compute the length of the diagonal.

${d}^{2} = {15}^{2} + {8}^{2}$

$\therefore d = \sqrt{225 + 64} = 17$

Note we do not consider the negative square root value since the diagonal is a length so cannot be negative.