Angle
Class 6 Maths · Chapter 2: Lines and Angles · NCERT Ganita Prakash section 2.5
Learn
An angle is made by two rays that start from the same point. That common point is the vertex, and the two rays are the arms of the angle.
We name an angle with a point on each arm and the vertex in the middle: ∠DBE or ∠EBD. When only one angle is at B, we may simply say ∠B. The small curve at the vertex shows which angle we mean.
∠DBE = ∠EBD
An angle's size is how much one arm must turn about the vertex to land on the other arm. As Aditya opens his laptop lid wider and wider, the angle grows.
Try it: turn the coral arm. More turn makes a bigger angle.
Angles are all around us: the blades of open scissors, the arms of a compass, an open door, and the hands of a clock.
Remember
- Two rays that start at the same point (the vertex) make an angle. The rays are its arms.
- Name an angle with the vertex in the middle: ∠DBE.
- How big an angle is = how far one arm turns to reach the other.
Quick check
In ∠PQR, which point is the vertex?
- P
- Q
- R
- PR
Answer
Q. The vertex is always the middle letter: Q.
Think about it
If three angles all have their vertex at P, why can't we call one of them just ∠P?
One answer
∠P would not tell which of the three angles we mean. We need a point on each arm, like ∠APB.
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.