cot-1(ab+1a-b)+cot-1(bc+1b-c)+cot-1(ca+1c-a)=
(1)
Ans. 0
Explanation:
cot-1(ab+1a-b)+cot-1(bc+1b-c)+cot-1(ca+1c-a)
=tan-1(a-bab+1)+tan-1(b-c1+bc)+tan-1(c-a1+ca)
=tan-1a-tan-1b+tan-1b-tan-1c+tan-1c-tan-1a=0