A right angle is an angle of 90 degrees. An acute angle is an angle less than 90 degrees. An obtuse angle is an angle greater than 90 degrees but less than 180 degrees.
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1, right angle
A right angle is an angle of 90 degrees, that is, the angle formed by two intersecting straight line segments is 90 degrees. In plane geometry, right angles are usually represented by symbols ∠ ABC = 90 or ∠ ABC = 90. Right angles have many uses. For example, in trigonometric functions, the definitions of functions such as sine, cosine and tangent need to be described by right angles.
2. acute angle
Acute angle refers to an angle less than 90 degrees, that is, the angle formed by two intersecting straight line segments is less than 90 degrees. In plane geometry, the symbol "∞" or "?" Usually used for acute angles. Say, where "?" Indicates an acute angle, and "∞" indicates other acute angles. Acute angle has many application scenarios in mathematics. For example, a triangle is an acute triangle if all three angles are acute.
3, obtuse angle
An obtuse angle refers to an angle greater than 90 degrees but less than 180 degrees, that is, the angle formed by two intersecting straight line segments is greater than 90 degrees but less than 180 degrees. In plane geometry, obtuse angles are often represented by ∞ symbols, such as ∠ ABC = 120. There are also many application scenarios of obtuse angles. For example, in a triangle, if one of the angles is obtuse, then the triangle is obtuse.
4. Right triangle
A right triangle is a triangle with an angle of 90 degrees. A right triangle has many important properties, such as Pythagorean theorem: in a right triangle, three sides satisfy the relationship of A 2+B 2 = C 2, where A and B are right angles and C is hypotenuse.
5. Angle dividing line
Angular bisector refers to a straight line segment that bisects an angle, and this straight line segment contains the same angle. In mathematics, bisector is often used to prove various geometric theorems, such as the angle between two parallel lines is equal to the corresponding angle between the straight lines they cut.