Triangle PQR is right angled at angle PQR and has sides of lengths 5 centimeter, 12 centimeter and 13 centimeters. Let us compute the sum of the square of the two smaller sides PQ and QR.
5 squared plus 12 squared gives 25 plus 144 which equals 169.
The square of the longest side PR is
13 squared which is 169.
Thus here again we see that the sum of the two smaller sides of a right triangle is equal to the square of the longest side of the triangle. The longest side, which is always opposite the right angle in the triangle, is called the hypotenuse of the triangle