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**rptamin****Member**- Registered: 2014-07-02
- Posts: 3

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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**rptamin****Member**- Registered: 2014-07-02
- Posts: 3

Please help,I need a few tips, I am not getting anywhere with it.

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**bob bundy****Moderator**- Registered: 2010-06-20
- Posts: 6,337

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

You cannot teach a man anything; you can only help him find it within himself..........Galileo Galilei

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