Pythagoras' Theorem

In a right angled triangle, the square on the hypotenuse is equal to the sum of the squares on the sides containing the right angle.

ABC is a triangle with ÐBAC = 90^o.

BC² = AB² + AC².

On AB, BC and CA as sides, describe squares ABFG, BCDE and ACKL respectively.

Draw AMN parallel to BE meeting BC at M and DE at N.

Join FC and AE.

Converse of Pythagoras' Theorem

If the square on one side of a triangle is equal to the sum of the squares on the other two sides, the angle contained by these two sides is a right angle.

In DABC, if BC² = AB² + AC² then, ÐA is a right angle.