Law of cosine is : c^2 = a^2 + b^2 − 2ab cos(theeta) so in case of right triangle , angle is 90 degree: putting 90 degrees into formula: c^2 = a^2 + b^2 − 2ab cos(90) As we know that: cos90 = 0 c^2 = a^2 + b^2 − 2ab (0) c^2 = a^2 + b^2 - 0 c^2 = a^2 + b^2 ( this is pythagorean theorem ). So the above statement is True.
