Q.

cot-1(ab+1a-b)+cot-1(bc+1b-c)+cot-1(ca+1c-a)=

1 0  
2 1  
3 π4  
4 -1  

Ans.

(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