tanA*sinA=sin^2 A/cosA=1-cos^2 A/cosA2tanAsinA=3就化为1-cos^2 A/cosA=3/2就化为2cos^2 A+3cosA-1=0令t=cosA那么就有2t^2+3t-2=0然后就有(2t-1)(t+2)=0解得t=1/2,t=-2(舍去)所以cosA=1/2结合(-π/2...