Page 266 - Start Up Mathematics_6

2. With B and C as centres, draw two arcs in C D
the interior of the angle cutting each other
at point D.

A B

D
3. Join A and D to obtain the bisector of ∠A.

A
Angles of Special Measures
There are angles which can be constructed without the use of protractor. These can be constructed
with the help of ruler and compass only. In fact one can verify the accuracy of these results.

Construction of an angle of measure 60°

1. Draw a ray OX.
O X

2. With O as centre, draw an arc of any radius
cutting OX at A. O A X

B
3. With A as centre and same radius, draw an
arc cutting the previously drawn arc at B.
O A X

Y
4. Join O and B to obtain an angle of measure
60°, i.e., ∠XOY = 60°. B

O A X

• An angle of 30° can be obtained by first constructing an angle of measure 60° and then bisecting it.
• An angle of 120° can be obtained by first constructing an angle of measure 60° and then doubling it.

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