Angle construction-upper primary mathematics

Constructing Angles of 60º, 120º, 30º, 15⁰, 90º and 45⁰

How to construct an angle of 60⁰.

(i) Draw a line and select point A.

(ii) With a compass placed at A make an arc BC.

(iii) Without adjusting the compass, place the compass at B and make an arc A-D to intersect with arc BC at E

(iv) Connect A to E and angle BAE = 60⁰

How to construct angle 30⁰

By bisecting angle 60⁰.

(i) Construct angle 60⁰ as in (a) and bisect it as follows

(ii) Place a compass at E and make an arc FG

(iii) Without adjusting the size of compass; place it at B and make an arc HI to intersect at J

(iv) Draw a line from A through J

(v) Angle JAB = 30⁰

 

How to prepare angle 15

By bisecting angle 30⁰

(ii) Place a compass at K and make an arc NO

(iii) Without adjusting the size of compass; place it at B and make an arc LM to intersect at P

(iv) Draw a line from A through P

(v) Angle JAB = 15⁰

How to prepare 120⁰

120⁰ = 180⁰ – 60⁰

How to construct angle 90⁰

• Draw a straight line and mark points AB
• Place a compass at point A and make arcs 1-2 and 3- 4
• Without adjusting the compass, place it at point B and make arcs 5-6 and 7- 8
• Draw through the intersection of arcs at C and D to meet line AB at E
• Angle CEB = 90⁰.

Or

• Draw a line and mark point A
• Using a compass mark points B and C equidistant from A
• Place a compass  at point B and make an arc 1-2.
• Without adjusting the length of a compass, place it at C and make an arc 3-4 to intersect with arc 1-2 at D.
• Draw a line at A through D
• Angle DAC = 90⁰.

 

How to prepare 45⁰

By bisecting angle 90⁰

• Prepare an angle 90⁰
• Place a compass at E and mark points F and G.
• Place a compass at F and make an arc 9-10.
• Without adjusting the compass place it at G and make an arc 11- 12 to intersect with arc 9 – 10 at H.
• Connect E to H
• Angle HEG = 45⁰

 

How to bisect a line AB

• Place a protractor at A and make arcs 1-2 and 3-4.
• Without adjusting the size of the compass place it at B and arc 5-6 to intersect arc 1-2 at C; then make arc 7-8 to intersect arc 3-4 at D.
• Draw a perpendicular bisector through C and D.

To try out some numbers by down load PDF below

Angle construction- upper primary

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Compiled by Dr. Bbosa Science +256 778 633 682

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