An angle less than 90 degrees is an acute angle, and an angle greater than 90 degrees is an obtuse angle. The so-called angle refers to the internal area of the space surrounded by two rays. This angle can be measured in degrees. A complete circle is divided into 360 equal parts, each equal part is 1 degree. According to the size of the angle, the angle can be divided into acute angle, right angle, obtuse angle and flat angle.

Among these four types, angles less than 90 degrees are called acute angles. An acute angle means that the included angle between two rays is very small and close to form a straight line. An acute angle is characterized by a sharp internal area and a relatively short distance between two rays. Based on the right angle, the degree of acute angle varies from 0 to 89 degrees.

Acute angle, a mathematical concept, refers to an angle greater than (0) and less than right angle (90). All three angles of an acute triangle are acute angles, and the sum of the internal angles of an acute triangle is 180. An obtuse angle is an angle greater than a right angle (90) and less than a right angle (180). The obtuse angle consists of two rays, which is one of the secondary angles and must be the second quadrant angle.

An angle greater than 90 degrees is called an obtuse angle. Oblique angle means that the included angle between two rays is large and close to form a ray. The obtuse angle is characterized by a wide internal area and a relatively long distance between two rays. Based on the right angle, the degree of obtuse angle varies from 9 1 degree to 179 degree.

Understanding the concepts of acute angle and obtuse angle needs to start from a geometric point of view. In geometry, the angle determines the angle between two rays. The division of acute angle and obtuse angle is determined according to the size of the angle. By observing the angle between two rays, we can directly judge the type of angle, and then judge the position and nature of the angle.

To sum up, an angle less than 90 degrees is an acute angle, indicating that the included angle between rays is relatively small; An angle greater than 90 degrees is an obtuse angle, indicating that the included angle between rays is relatively large. Understanding these basic concepts can help us better understand and apply the concept of angle in geometry.