In ` A B C ,cotA/2+cotB/2+cotC/2` is equal to `/(r^2)` (b) `((a+b+c)^2)/(a b c)2R` (c) `/r` (d) `/(R r)`

Explanation

Here, we will use,

`cot (A/2) = sqrt((s(s-a))/((s-b)(s-c))) and sin(A/2) = sqrt(((s-b)(s-c))/(bc))`

Now, `L.H.S. = (cot (A/2) +cot (B/2))(asin^2(B/2) + bsin^2(A/2))`

`=(sqrt((s(s-a))/((s-b)(s-c))) + sqrt((s(s-b))/((s-a)(s-c))))(a((s-a)(s-c))/(ac)) +b((s-b)(s-c))/(bc))`

`=sqrts[(s-a+s-b)/(sqrt((s-a)(s-b)(s-c)))](s-c)/c[s-a+s-b]`

`=sqrts[(c(s-c))/(sqrt((s-a)(s-b)(s-c)))]`

`=csqrt((s(s-c))/((s-a)(s-b)))`

`=c cot(C/2) = R.H.S.`