(i) Angle – A shape formed by two lines or rays diverging from a common vertex.

Types of angle: (a) Acute angle (less than 90°)

(b) Right angle (exactly 90°)

(c) Obtuse angle (between 90° and 180°)

(d) Straight angle (exactly 180°)

(e) Reflex angle (between 180° and 360°)

(f) Full angle (exactly 360°)

(ii) Interior of an angle – The area between the rays that make up an angle and extending away from the vertex to infinity.

The interior angles of a triangle always add up to 180°.

(iii) Obtuse angle – It is an angle that measures between 90 to 180 degrees.

(iv) Reflex angle – It is an angle that measures between 180 to 360 degrees.

(v) Complementary angles – Two angles are called complementary angles if the sum of two angles is 90°.

(vi) Supplementary angles – Angles are said to be supplementary if the sum of two angles is 180°.