Find the length of the diagonal of a rectangle whose sides are 12 cm

Using Pythagoras theorem :

$A D^{2}+D C^{2}=A C^{2}$

$5^{2}+12^{2}=A C^{2}$

$25+14=A C^{2}$

$169=A C^{2}$

$A C=\sqrt{169}$

$=13 \mathrm{~cm}$

Thus, length of the diagonal is $13 \mathrm{~cm}$.