The longest side in a right-angled triangle is 12cm. One of the shorter sides is 4 cm. Calculate the perimeter of the triangle

12² = 4² + x² [This is pythagoras' theorem (a² = b² + c²) ]
144 =16 + x ^2
128 = x²
11.31 = x
Perimeter = 11.31 + 12 +4 = 27.31