Definitions [5]
Complementary angles: When the sum of the measures of two angles is 90°, the angles are called complementary angles. Example, 30° + 60° = 90°.
Supplementary angles: When the sum of the measures of two angles is 180° are called supplementary angles. Example, 60° + 120° = 180°.
Opposite Rays: Two rays which have a common origin and form a straight line are said to be opposite rays.
Linear pair: A linear pair is a pair of adjacent angles whose non-common sides are opposite rays.
Definition: Exterior Angle
An exterior angle is formed when a side of a triangle is extended beyond its vertex. The angle created between the extended side and the adjacent side of the triangle is the exterior angle.
Formulae [1]
Formula: Sum of Interior Angles
Sum of interior angles of a polygon = (n – 2) × 180°
Explanation:
- A polygon with n sides can be divided into smaller triangles by drawing diagonals from one vertex.
- Each triangle has a total angle sum of 180°.
- Since the number of triangles formed inside the polygon is (n – 2).
- The total sum of all interior angles is therefore (n – 2) × 180°.
