= (s – a) tan A/2
= (s – b) tan B/2
= (s – c) tan C/2
= [a sin (B/2) sin (C/2)]/ cos A/2
= [b sin (A/2) sin (C/2)]/ cos B/2
= [c sin (B/2) sin (A/2)]/ cos C/2
= 4R sin A/2 sin B/2 sin C/2
r1 = Δ/s-a, r2 = Δ/s-b, r3 = Δ/s-c
r1 = s tan A/2, r2 = s tan B/2, r3 = s tan C/2
r1 = [a cos (B/2) cos (C/2)]/ cos A/2
r2 = [b cos (C/2) cos (A/2)]/ cos B/2
r3 = [c cos (A/2) cos (B/2)]/ cos C/2
OA = 2R cos A
OB = 2R cos B
OC = 2R cos C
The circum radius of the pedal triangle = R/2
The area of the pedal triangle is = 2Δ cos A cos B cos C
tan A/2 tan B/2 = (s-c)/s
tan A/2 + tan B/2 = c/s cot C/2 = c(s-c)/Δ
tan A/2 - tan B/2 = (a-b)(s-c)/Δ
cot A/2 + cot B/2 = (tan A/2 + tan B/2)/ (tan A/2.tan B/2)
= c/(s-c) cot C/2
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