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D E F is the triangle formed by joining ...

`D E F` is the triangle formed by joining the points of contact of the incircle with the sides of the triangle `A B C ,\ ` prove that its sides are `2rcosA/2,\ 2rcosB/2\ a n d\ 2rcosC/2` where `r` is the radius of incircle of ` A B Cdot` its angles are `pi/2-A/2,pi/2-B/2a n dpi/2-C/2` its area is `(r^2s)/(2R)` where `' s '` is the semiperimter and `R` is the circumradius of the ` A B C` .

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