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#1 2017-03-18 02:52:19
- !nval!d_us3rnam3
- Member
- Registered: 2017-03-18
- Posts: 46
Help me; need answer before tonight. Thanks!
Let the incircle of triangle $ABC$ be tangent to sides $\overline{BC}$, $\overline{AC}$, and $\overline{AB}$ at $D$, $E$, and $F$, respectively. Prove that triangle $DEF$ is acute.
I have tried proving that triangle DEF's angles were less than the opposite angles in triangle ABC, but that wasn't really complete. Can anyone help? Thanks! 
"If we wanna be great, we can't just sit on our hands" - 2017 NFL Bears draft
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#2 2017-03-18 05:42:32
- bobbym
- bumpkin
- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606
Re: Help me; need answer before tonight. Thanks!
In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.
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#3 2017-03-18 09:03:01
- !nval!d_us3rnam3
- Member
- Registered: 2017-03-18
- Posts: 46
Re: Help me; need answer before tonight. Thanks!
Thank you so much for helping! 
"If we wanna be great, we can't just sit on our hands" - 2017 NFL Bears draft
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#4 2017-03-18 11:05:07
- bobbym
- bumpkin
- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606
Re: Help me; need answer before tonight. Thanks!
Hi;
Hopefully, it will inspire you to learn more math and spread that to others. Welcome to the forum.
In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.
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