# Class 6 Maths Chapter 5 Exercise 5.4 Pdf Notes NCERT Solutions

Class 6 Maths Chapter 5 Understanding Elementary Shapes Exercise 5.4 pdf notes:-

Exercise 5.4 Class 6 maths Chapter 5 Pdf Notes:-

## Ncert Solution for Class 6 Maths Chapter 5 Understanding Elementary Shapes Exercise 5.4 Tips:-

Measuring Angles
The improvised â€˜Right-angle testerâ€™ we made is helpful to compare angles with
a right angle. We were able to classify the angles as acute, obtuse or reflex.
But this does not give a precise comparison. It cannot find which one among
the two obtuse angles is greater. So in order to be more precise in comparison,
we need to â€˜measureâ€™ the angles. We can do it with a â€˜protractorâ€™.
The measure of angle
We call our measure, â€˜degree measureâ€™. One complete revolution is divided
into 360 equal parts. Each part is a degree. We write 360Â° to say â€˜three hundred
sixty degreesâ€™.
Think, discuss and write
How many degrees are there in half a revolution? In one right angle? In one
straight angle?
How many right angles make 180Â°? 360Â°?

Fold it twice to get a shape as shown. This is

1. Open it out. You will find a
semi-circle with a fold in the
middle. Mark 90o

on the fold.

1. Fold the semicircle to

once more as shown. The angle is half of
90o
i.e. 45o

Open it out now. Two folds appear on each side. What
is the angle upto the first new line? Write 45o
on the

first fold to the left of the base line.

1. The fold on the other side would be 90o
• 45o
= 135o
1. Fold the paper again upto 45Â° (half of the
quadrant). Now make half of this. The first
fold to the left of the base line now is half of
45Â° i.e. 22 1
2
o
. The angle on the left of 135o

would be 157 1
2
o
.

You have got a ready device to measure angles. This is an approximate
protractor.

The Protractor
in your â€˜instrument boxâ€™. The curved
edge is divided into 180 equal parts.
Each part is equal to a â€˜degreeâ€™. The
markings start from 0Â° on the right side
and ends with 180Â° on the left side, and
vice-versa.
Suppose you want to measure an angle ABC.

1. Place the protractor so that the mid point (M in the figure) of its
straight edge lies on the vertex B of the angle.
2. Adjust the protractor so that BC is along the straight-edge of the protractor.
3. There are two â€˜scalesâ€™ on the protractor : read that scale which has the
0Â° mark coinciding with the straight-edge (i.e. with ray BC
).
4. The mark shown by BA on the curved edge gives the degree measure of
the angle.
We write m âˆ ABC= 40Â°, or simply âˆ ABC= 40Â°.

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