The first volume of eighth grade mathematics. The trilateral relationship of right triangle is the teaching content of the first volume of eighth grade mathematics. The sum of squares of two right-angled sides of a right-angled triangle is equal to the square of the hypotenuse (Pythagorean theorem). In a right triangle, if an angle is equal to 30 degrees, then the right side opposite to the 30-degree angle is half of the hypotenuse. Inverse Theorem of Pythagorean Theorem: A triangle is a right triangle if its three sides A, B and C satisfy a2+b2=c2.