Special Types of Angles
Class 6 Maths · Chapter 2: Lines and Angles · NCERT Ganita Prakash section 2.8
Learn
Imagine a door. When Aditi swings it all the way round back to where it started, that is a full turn. When it opens to point exactly the other way, that is a half turn: the two arms make one straight line, a straight angle.
Fold the paper so that arm OB lies on arm OA. The crease divides the straight angle into two equal angles. Each one is a right angle. So a straight angle holds two right angles.
A right angle is a quarter turn and looks like the letter L. Two lines that meet at a right angle are called perpendicular lines.
Angles smaller than a right angle are acute (acute means sharp). Angles bigger than a right angle but smaller than a straight angle are obtuse (obtuse means blunt).
Make a right angle: turn the coral arm until it makes an L.
Remember
- Full turn: all the way round. Straight angle: half a turn, the arms in one straight line.
- Right angle: a quarter turn, half of a straight angle, shaped like L. Perpendicular lines meet at a right angle.
- Acute: smaller than a right angle. Obtuse: between a right angle and a straight angle.
Quick check
How many right angles make a straight angle?
- 1
- 2
- 3
- 4
Answer
2. Folding a straight angle in half gives two equal right angles.
Think about it
How many right angles can you find in a classroom window with 4 glass panes?
One answer
Each rectangular pane has 4 right angles at its corners: 4 × 4 = 16. There are even more where the frames cross!
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.