Angles

When two rays meet at a common point, an angle is formed. This common point is called a Vertex. Each of these rays is called an Arm of the angle.

In the above figure AB and AC are the two rays and BAC is the angle formed between them.

The space within the arms of an angle, produced indefinitely is called the Interior of the angle. The space outside the arms of an angle, produced indefinitely is called the Exterior of the angle. If two angles have a common arm, a common vertex, and lie on either side of the common arm are called Adjacent angles.

Types of Angles Altitude of a triangle is a straight line passing through a vertex and perpendicular to the opposite side. This opposite side is called the base of the altitude and the point where the altitude intersects the base is called the foot of the altitude. The three altitudes of a triangle intersect in a single point called the orthocentre of the triangle. The orthocentre lies inside the triangle if and only if the triangle is acute.

Angle bisector

• Right Angle : An angle of magnitude exactly 90° is called a right angle.

• Straight Angle : When the arms of an angle are opposite rays forming a straight line, the angle thus formed is called a straight angle. Its measure is 180°.
• Acute Angle : An angle of magnitude less than a right angle is called an acute angle.
• Obtuse Angle : An angle of magnitude greater than a right angle is called an obtuse angle.
• Zero Angle : An angle of magnitude zero is called zero angle. Meaning is that there is no angle between the rays.
• Complete Angle : An angle of magnitude 360° is called a complete angle. That is when a ray makes a complete revolution, a complete angle is formed.
• Reflex Angle : An angle of magnitude more than 180° and less than 360° is called a reflex angle.

The above discussed are the different types of angles generally