Hinglish

Types of Angles and their Measures

Class 6 Maths · Chapter 2: Lines and Angles · NCERT Ganita Prakash section 2.11

Learn

Now we can describe each type by its measure. Acute angle: more than 0° and less than 90°.

Right angle: exactly 90°. Obtuse angle: more than 90° and less than 180°.

Straight angle: exactly 180°. Reflex angle: bigger than 180° but smaller than 360°, going the long way round.

∠REB is a straight angle (180°) and ∠TER = 80°. So the other part, ∠BET, is 180° − 80° = 100°.

180° − 80° = 100°

Make a reflex angle: turn the arm past the straight line.

A bicycle wheel has 36 spokes, spaced equally. They share the full turn, so two spokes next to each other make 360° ÷ 36 = 10°.

360° ÷ 36 = 10°

Remember

  • Acute: 0°–90°. Right: 90°. Obtuse: 90°–180°. Straight: 180°. Reflex: 180°–360°.
  • Parts of a straight angle add up to 180°; parts of a full turn add up to 360°.

Quick check

An angle of 200° is …

  1. Acute
  2. Obtuse
  3. Straight
  4. Reflex
Answer

Reflex. 200° is past a straight angle (180°) but not yet a full turn (360°), so it is reflex.

Think about it

Puzzle: double me and I become a straight angle. What am I? What do I become if you halve me?

One answer

A straight angle is 180°, so I am 180° ÷ 2 = 90°, a right angle. Half of me is 45°, an acute angle.

Practice

Practise with fresh questions at three levels (easy, medium, hard), some answered hands-on, with hints and worked answers. Get 4 of your last 5 right to finish the topic.