Prove that tan−1(1)+tan−1(2)+tan−1(3)=π.Answer: Proved: the sum equals π.Solutiontan−1(1)=4π. For tan−12+tan−13, the product 2⋅3=6>1 with both positive, sotan−12+tan−13=π+tan−11−2⋅32+3=π+tan−1−55=π+tan−1(−1)=π−4π=43πHencetan−11+tan−12+tan−13=4π+43π=ππCBSE Class 12 Board · 2010 · Subjective