Angles in any type of triangle always have a sum of 180 degrees.

The proof of this includes a straight line and knowing how angles interact with parallel and perpendicular lines. I would recommend further investigation on youtube as it is much easier to understand it visually.

The right triangle has one 90 degrees angle and two acute (< 90 degrees) 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.