How to recognize right angles, acute angles and obtuse angles

The distinction between right angles, acute angles, and obtuse angles: The definition of right angles in "Elements of Geometry": When the adjacent angles formed by a straight line and another horizontal straight line are equal to each other, each of these angles is called a right angle. , and this straight line is said to be perpendicular to another straight line. In geometry and trigonometry, a right angle, also called a positive angle, is an angle with an angle of 90 degrees. It is relative to a quarter of a circle (that is, a quarter of a circle), and two right angles equal a half angle (180°). An angle smaller than a right angle is called an acute angle, and an angle larger than a right angle but smaller than a straight angle is called an obtuse angle. A right angle is equal to 90 degrees, symbol: Rt∠. Acute angle refers to an angle greater than 0° and less than 90° (right angle). Acute angles are minor angles. The sum of two acute angles is not necessarily greater than a right angle, but it is always less than a straight angle. An acute angle must be the first quadrant angle, and the first quadrant angle is not necessarily an acute angle. Obtuse angle An obtuse angle is an angle that is greater than a right angle (90°) and less than a straight angle (180°).