Prove that cot-1(13) + cot-1(21) + cot-1(-8) = pi Share with your friends Share 1 Vipin Verma answered this cot-113+cot-121+cot-1-8=cot-113 +tan-1121+tan-1(-18)=cot-113 +tan-1121-181+12118=cot-113 +tan-1-13168169168=cot-113 +tan-1-13169=cot-113 +tan-1-113=cot-113+cot-1(-13)=cot-113+π-cot-113=π hence Proved 7 View Full Answer
