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#1 2015-01-29 08:00:31

SPARKS_CHAN
Member
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.

b41e27615573c2236144dc034d7cdcde5817fec0.png

I believe these are similar triangles...

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#2 2015-01-29 20:10:27

Bob
Administrator
Registered: 2010-06-20
Posts: 10,053

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 smile

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