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#1 2015-01-29 08:00:31
- SPARKS_CHAN
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- Registered: 2014-12-05
- Posts: 15
Help with proof
Let the incircle of triangle ABC be tangent to sides BC, AC, and AB at D, E, and F, respectively. Prove that triangle DEF is acute.
I believe these are similar triangles...
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#2 2015-01-29 20:10:27
- Bob
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- Registered: 2010-06-20
- Posts: 10,626
Re: Help with proof
hi SPARKS_CHAN,
Mark the centre of the circle as point O.
The angle at the centre of any circle is twice the angle at the edge, made by the same chord.
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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