In mathematics, the Pythagorean Theorem, also known as Pythagoras's theorem, is a fundamental relation in Euclidean geometry among the three sides of a right triangle. It states that the area of the square whose side is the hypotenuse is equal to the sum of the areas of the squares on the other two sides. The Pythagorean Theorem consists of a formula a^2+b^2=c^2 which is used to figure out the value of (mostly) hypotenuse in a right triangle. The a and b are the 2 "non-hypotenuse" sides of the triangle (Opposite and Adjacent). Note that the Pythagorean Theorem only works with right triangles. You can use the Pythagorean Theorem to find the length of the hypotenuse of a right triangle if you know the length of the triangle's other two sides, called the legs. Put another way; if you know the lengths of a and b, you can find c. Chapter 15 helps students understand the types of triangles based on the angles and length of sides.