prove that ; cot^-1[ab+1/a-b] + cot ^-1 [bc +1/b-c ] +cot ^-1[ca +1/c-a] = 0?

prove that ; tan ^-1 [cos x/ 1-sin x ] - cot ^-1 [√1+cosx /1-cosx ] = π/4 cot^-1[ab+1/a-b] + cot ^-1 [bc +1/b-c ] +cot ^-1[ca +1/c-a] = 0