I just need help starting it off. Write an indirect proof proving only one angle of an obtuse triangle is greater than 90°.

Question

anonymous · Answer

@ganeshie8 Can you help me please?

anonymous · Answer

@timo86m

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@johnweldon1993

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@helpme1.2

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@iheartfood please help?

anonymous · Answer

You first have to assume the opposite of what you are trying to prove.

ranga · Answer

Assume two angles of an obtuse triangle is greater than 90 degrees each.  The sum of these two angles will be greater than 180 degrees.  This cannot be true because the sum of all three angles of a triangle is 180 degrees.  Therefore, the assumption that two angles of an obtuse triangle is greater than 90 degrees each is wrong.  

The same proof applies if we assume all three angles of an obtuse triangle are greater than 90 degrees each because the sum will be greater than 270 degrees but the sum of all three angles of a triangle is 180 degrees.   Therefore, the assumption that three angles of an obtuse triangle is greater than 90 degrees each is wrong.  

Therefore, only one angle of an obtuse triangle can be greater than 90 degrees.

anonymous · Answer

:/ I forgot to close this and i accidently bumped it. But i did read your reply and it did help me understand a little bit more.