3 Questions around this concept.
In a triangle with sides ( which are the ex-radii) then:
Escribed Circle of Triangle
The circle which touches the side BC and two sides AB and AC produced of triangle ABC is called the escribed circle opposite to the angle A. Its radius is denoted by r1. Similarly, r2 and r3 denote the radii of the escribed circles opposite to the angles B and C respectively.

Formulae for $r_1, r_2$ and $r_3$
1. $r_1=\frac{\Delta}{s-a}, r_2=\frac{\Delta}{s-b}, r_3=\frac{\Delta}{s-c}$
2. $r_1=s \tan \frac{A}{2}, r_2=s \tan \frac{B}{2}, r_3=s \tan \frac{C}{2}$
3. $r_1=4 R \sin \frac{A}{2} \cos \frac{B}{2} \cos \frac{C}{2}$
$r_2=4 R \cos \frac{A}{2} \sin \frac{B}{2} \cos \frac{C}{2}$
$r_3=4 R \cos \frac{A}{2} \cos \frac{B}{2} \sin \frac{C}{2}$
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Mathematics for Joint Entrance Examination JEE (Advanced) : Trigonometry
Page No. : 5.29
Line : 45
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