Grade 6 Lines and Angles Ex 2.4

1. How many right angles do the windows of your classroom contain? Do you see other right angles in your classroom?

Answer:

A rectangular window has 4 right angles.

 __________
|         |
|         |
|_________|

Each corner = 90°

Other right angles in classroom:

• Door corners
• Blackboard corners
• Book edges
• Table corners

2. Join A to the grid points in the figure by a straight line to get a straight angle.What are the different ways of doing it?
Answer:

A straight angle measures 180°.

(a) Horizontal Straight Angle

• • • • •
• • • • •
A───────B
• • • • •
• • • • •

Angle formed = 180°

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(b) Slanting Straight Angle

• • • • •
• • • • B
• • • ••
• • • •
A • • •

Angle formed = 180°

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3. Join A to other grid points in the figure by a straight line to get a right angle. What are the different ways of doing it?
Answer:

A right angle measures 90°.

(a) Horizontal and Vertical Lines

      B
      |
      |
A─────┘

Angle at A = 90°

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(b) Slanting Right Angle

      /
     /
A ──┘

Angle at A = 90°

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4. Get a slanting crease on the paper. Now, get another crease that is perpendicular to the slanting crease.

(a) How many right angles do you have now? Why justify that the angles are exact right angles.

Answer:

When two perpendicular creases meet, they form 4 right angles.

\  |  /
 \ | /
-- + --
 / | \
/  |  \

Each angle = 90°

They are exact right angles because perpendicular lines always meet at 90°.

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(b) Describe how you folded the paper so that any other person would understand how the present can simply obtain your description to get the right angle.
Answer:

1. Fold the paper slantwise to make one crease.

2. Fold the paper again so that the second crease crosses the first crease exactly at the middle.

3. Make sure both creases meet perpendicularly.

4. Open the paper to see four right angles.