Let the incircle of triangle ABC be tangent to sides, , and at , , and , respectively. Prove that triangle DEF is acute.
[Edited latex by admin]
Please help,I need a few tips, I am not getting anywhere with it.
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.