How do you use the Pythagorean Theorem to determine if the three sides are a right triangle: 9 in, 12 in, 15 in?
The three sides 9 in, 12 in, and 15 in do represent a right triangle.
The hypotenuse is the greatest length. So using the Pythagorean theorem, which states
Since the square of the hypotenuse is equal to the sum of the squares of the other two sides, this is a right triangle.