Answer:

hope it will help you

Step-by-step explanation:

since these parts produce tangent at the circle

hence,

PP =AQ

CP =CR

BR = BQ

Given,

AB =C

AC = B

BC = A

since CPOR is square hence

CP = CR = r

BR = BC - CR = a- r

BQ = BR = a- r

similarly,

AP = AC - CP = b- r

AQ= AP = b - r

Now,

AB = C

AQ + BQ = C

b - r + a - r = c

b + a - 2r = c

2r = a+b+c

which is the required equation!!!!!