In a right angled triangle we can use Pythagoras theorem to determine third side in case two sides are given.
The formula of Pythagoras theorem is given by:
Where x , y and z are sides of triangle , z is hypotenuse.
Now we use this formula to find hypotenuse.
Plugging other two sides which are 5 in. and 12 in.
Taking square root on both sides
square root of 169 is 13
so we have z=13
Hypotenuse is 13 inches.