Prove that : tan-1(1/4) + tan-1(2/9) = 1/2 Cos-1 (3/5) Share with your friends Share 29 Manmeet Singh answered this To prove: LHS:This can be written as: = RHSHence proved. 67 View Full Answer Jyoti Dua answered this L.H.S = tan-1(1/4)+tan-1(2/9) = tan-1(1/4+2/9)/(1-1/4*2/9) = tan-1(1/2) = 1/2*2tan-1(1/2) = 1/2cos-1(1-1/4)/(1+1/4) = 1/2cos-1(3/5) -12