The law of cosines reduces to the pythagorean theorem when the triangle is right.
truth or false?

The law of cosine is generally expressed as, 
                                 c² = a² + b² - 2ab x (cos C)
If the triangle is right (one of the angles measures 90 degrees, in this case C), the equation becomes, 
                                c² = a² + b² - 2ab x (cos 90)
Since cos 90 is zero, this equation reduces to c² = a² + b². This equation is the general form of the Pythagorean theorem. Thus, the answer is TRUTH.