2SIN A-SIN ACOS A-3COS A=0两边同时除以cosA*cosA2tan^2(A)-tanA-3=0tanA=-1或tanA=3/2.A=-π/4 或3π/4或{sinA=3/√13和cosA=2/√13}SIN(A+π/4)/SIN 2A+COS 2A+1(1)A=-π/4 ,=1(2)A=3π/4 ,=1(3){sinA=3/√13和co...