The answer I got is

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∠ABD=38°,∠DBC=46°,∠BCA=22°,∠ACD=48°,

 then find ∠BDA

Asked 10 years, 2 months ago

Modified 9 years, 7 months ago

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I'm interested in Langley's problem.

I've been struggling to solve the following question and I've just got the result by a tedious calculation using Euler's formula eiπx/180=cosx°+sinx°

.

In a convex quadrilateral ABCD

, letting ∠ABD=38°,∠DBC=46°,∠BCA=22°,∠ACD=48°,

 then find ∠BDA

.

The answer I got is ∠BDA=18°

. Then, here is my question.

Question: Could you show me how to prove this by the way of elementary geometry?

I've tried, but it seems very difficult.

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