When the triangle has a right angle (90°) ...... and squares are made on each of the
three sides, then ...
... the biggest square has the exact same area as the other two squares put together  it 
 is called "Pythagoras' Theorem" and can be written in one short equation:

a2 + b2 = c2 ..........
1 5 1
Pythagoras Theorem states that the sum of the squares of the adjacent sides of the right angle of a right angled triangle is equal to the square of the hypoteneous(the longest side opposite to the right angle triangle) i.e. the third side.

AB² + BC² = AC²
1 5 1