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I am puzzled by this question.

I tried all triangle angle formulas, and every time I end up reaching x + y = 130.

enter image description here

I am sure I am missing one essential property. If anybody please solve this and possibly remind me of which property I forgot to use.

codingenious
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  • It was in my notebook. :| Updated the picture. – codingenious Sep 28 '16 at 19:04
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    http://math.stackexchange.com/questions/6942/finding-an-angle-within-an-80-80-20-isosceles-triangle – Jean-Claude Arbaut Sep 28 '16 at 19:07
  • This is sometimes called Langley's problem. The question is answered at least once on this site here: http://math.stackexchange.com/questions/6942/finding-an-angle-within-an-80-80-20-isosceles-triangle – Mark Fischler Sep 28 '16 at 19:07
  • This is a very famous problem and you can check the answer at this site: http://www.cut-the-knot.org/triangle/80-80-20/60-70Sol1.shtml – Seyed Sep 28 '16 at 19:57

1 Answers1

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Here is the general solution to this problem. enter image description here

Seyed
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