Question

The longest side of a right triangle is 15 cm long another side is 12 cm long what is the length of the third side

Answer 1

The question is tricky. But any way the longest side of a right triangle is always the hypotenuse. So we know the hypotenuse if 15 cm. 
Now, consider the Pythagorean theorem: 
a^2 + b^2 = h^2, where a and b are the sides of a right triangle and h is the hypotenuse. 
We know one side is 12cm and the hypotenuse is 15 cm, so: 
12^2 + b^2 = 15^2, or 144 + b^2 = 225 
subtract 144 from either side to get 
b^2 = 225 - 144 = 81 
now take the square root of either side to get 
b = 9 
The third side is 9 cm