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http://www.explorelearning.com/ELContent/gizmos/ELMath_Deliverable/ExplorationGuides/Geometry/images/EL_GEO_TriSum6.gif

A. mangle1 = 43°, mangle2 = 137°

B. mangle1 = 137°, mangle2 = 43°

C. mangle1 = 43°, mangle2 = 47°

D. mangle1 = 79°, mangle2 = 101°

laurent dormeus
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  • Welcome to Math.SE! What have you tried so far to answer the problem? – Eoin Nov 11 '14 at 19:19
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    What do you know about the sum of angles in any triangle? And what do you know about supplementary angles? – Timbuc Nov 11 '14 at 19:20

1 Answers1

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enter image description here

Consider the image and read the proof. For every triangle, the sum of it's angles is $180º$. Moreover

enter image description here

We know that in the last figure $\angle b+\angle d = 180º=\angle a + \angle c + \angle b\Rightarrow \angle d = \angle c + \angle a$.

Apply this general results to your triangle and you will obtain the answer.

Vladimir Vargas
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  • Perhaps eliminating that $;m;$ in front of the angle sign will make things clearer. For example, compare $;\angle d = \angle c +\angle a;$ with $;m\angle d=m\angle c +m\angle a;$ – Timbuc Nov 11 '14 at 20:28
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    Done. I wrote it that way because of the first image. – Vladimir Vargas Nov 11 '14 at 20:29