The right triangle has one 90 degree angle and two acute (< 90 degree) angles. Since the sum of the angles of a triangle is always 180 degrees... The two sides of the triangle that are by the right angle are called the legs... and the side opposite of the right angle is called the hypotenuse.
An acute angle is an angle that measures less than 90 degrees. A triangle formed by all angles measuring less than 90˚ is also known as an acute triangle. For example, in an equilateral triangle, all three angles measure 60˚, making it an acute triangle.
