Construct an angle of 120° using compass - Ex 11.1

Construct an angle of 120° using compass - Part 2

Construct an angle of 120° using compass - Part 3

Construct an angle of 120° using compass - Part 4

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Construct an angle of 120° using ruler and compass Steps of construction Draw a ray OA. Taking O as center and any radius, draw an arc cutting OA at B. 3. Now, taking B as center and with the same radius as before, draw an arc intersecting the previously drawn arc at point C. 4. With C as center and the same radius, draw an arc cutting the arc at D 5. Join OD Thus, ∠AOD = 120° Justification We need to prove ∠ AOD = 120° Join OC and BC So, OB = BC = OC ∴ Δ OCB is an equilateral triangle ∴ ∠ BOC = 60° Join CD So, OD = OC = DC ∴ Δ DOC is an equilateral triangle ∴ ∠ DOC = 60° (Radius of equal arcs - By Construction) (Radius of equal arcs - By Construction) Thus, ∠ AOD = ∠ BOC + ∠ COD = 60° + 60° = 120° Hence verified

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Davneet Singh

Davneet Singh has done his B.Tech from Indian Institute of Technology, Kanpur. He has been teaching from the past 14 years. He provides courses for Maths, Science and Computer Science at Teachoo