1.3sinB=sin(2A+B)
3sin[(A+B)-A]=sin[(A+B)+A]
3sin(A+B)cosA-3cos(A+B)sinA=siin(A+B)cosA+cos(A+B)sinA
2sin(A+B)cosA=4cos(A+B)sinA
tan(A+B)=2tanA
2.(tanA+tanB)/(1-tanAtanB)=2tanA
tanA+tanB=2tanA-2tan^2A*tanB
tanB=tanA/(1+2tan^2A)=1/(1/tanA+2tanA) 1/tanA+2tanA>=2√2
>=1/(2√2)
tanB的最大值2√2
此时tanA=√2/2