In a triangle ABC, if r1,r2,r3 are the exradii, then bcr1+car2+abr3=k[∑sa−3], where k is equal to
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Solution
We have, bcr1+car2+abr3 =bc△s−a+ca△s−b+ab△s−c =bc(s−a)△+ca(s−b)△+ab(s−c)△ =1△[bcs−bca+cas−cab+abs−abc] =abc△[sa+sb+sc−3] =abc△[∑sa−3] On comparing with k[∑sa−3] we get k=abc△