British Geometry

Geometry Level 2

Given, in Δ \Delta ABC, ∠ \angle BAC= 60 ° \ang{60} . D is a point on BC which is one third of the way from C to B. If AD bisects ∠ \angle BAC , ∠ \angle ADB=?


The answer is 120.

Rajdeep Ghosh by Rajdeep Ghosh , 17, India

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1 solution

Rajdeep Ghosh
Mar 7, 2018

Use sine rule on both triangles Δ \Delta ADC and Δ \Delta ADB. Incorporate the length AD in both expressions.

Simplify and get a relation between ∠ \angle ACB and ∠ \angle ABC. Use angle sum property to find the latter.

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