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#1 2014-07-08 03:43:16
- rptamin
- Member
- Registered: 2014-07-02
- Posts: 3
Proof
Let the incircle of triangle ABC be tangent to sides
, , and at , , and , respectively. Prove that triangle DEF is acute.[Edited latex by admin]
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#2 2014-07-09 01:55:56
- rptamin
- Member
- Registered: 2014-07-02
- Posts: 3
Re: Proof
Please help,I need a few tips, I am not getting anywhere with it.
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#3 2014-07-25 08:22:33
- Bob
- Administrator
- Registered: 2010-06-20
- Posts: 10,143
Re: Proof
hi rptamin
Let O be the centre of the circle.
The incentre always lies inside the triangle => DOE < 180
By angle property => DFE < 90.
Ditto for the other two angles.
Bob
Children are not defined by school ...........The Fonz
You cannot teach a man anything; you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you! …………….Bob 
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