sin(π/4+a)cos[π/2-(π/4-a)]=1/42sin(π/4+a)cos(π/4+a)=1/2sin[2(π/4+a)]=1/2sin(π/2+2a)=1/2cos2a=1/2sin²2a+cos²2a=1所以sin2a=±√3/2tana-1/tana=sina/cosa-cosa/sina=(sin²a-cos²a)...