prove that sin3A+cos3A/1-2cos2A =secA-sinA/tanA -1 Share with your friends Share 1 Devesh Kumar answered this L.H.S=sin3A+cos3A1-2cos2A=sinA+cosAsin2A-sinAcosA+cos2Asin2A + cos2A-2cos2A As a3+b3=a+ba2-ab+b2 & 1=sin2A+cos2A =sinA+cosAsin2A-sinAcosA+cos2Asin2A - cos2A=sinA+cosAsin2A-sinAcosA+cos2AsinA+cosAsinA-cosA=1-sinAcosAsinA-cosA=1-sinAcosAcosAsinA-cosAcosA=secA-sinAtanA-1=R.H.SHence proved 4 View Full Answer
