a triangle ABC,if r1 is the exradius of the excircle opposite to A,r2is the exradius of the excircle opposite to B and r3is the exradius of the excircle opposite to C....In prove that(ar1+br2+cr3)/abc=(1/r)-(1/2R)where r is the inradius and R is the circum radius.solytion of trainle

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properties of triangles. in the following problem, In a triangle ABC,if r1 is the exradius of the excircle opposite to A,r2 is the exradius of the excircle opposite to B and r3is the exradius of the excircle opposite to C.... prove that (ar1+br2+cr3)/abc=(1/r)-(1/2R) where r is the inradius and R is the circum radius. i tried using these formulae: r1=(area of triangle)/(s-a) r1=stanA/2 but i cudnt solve it.how should i start?