## The 80-80-20 Triangle Problem, A Derivative, Solution #7

ABC is an isosceles triangle with vertex angle

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Copyright © 1996-2018 Alexander Bogomolny

This solution has been reported in [*Which Way Did the Bicycle Go?*].

Add a couple of triangles ACU and AUV equal to ΔABC and mark point F on AV,

∠ACE = ∠ECU - ∠ACU = 90° - 80° = 10°,

∠AEC = 180° - 20° - 10° = 150°.

### Reference

- J. Konhauser, D. Velleman, S. Wagon,
*Which Way Did the Bicycle Go?*, MAA, 1996, #15

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Copyright © 1996-2018 Alexander Bogomolny