sinB=sin(X+B-X)=sin(X+B)cosX-cos(X+B)sinXsin(2X+B)=sin(X+B+X)=sin(X+B)cosX+cos(X+B)sinX代入3sinB-sin(2X+B)=0得 2sin(X+B)cosX-4cos(X+B)sinX=02tan(X+B)-4tanX=0tan(X+B)-2tanX=0