y=f(x)=-sinx,因为f(a+π)=-sin(a+π)=sina=-2/3,则cosa=±√5/3,
sin2a=2*(-2/3)*(±√5/3)=±4√5/9,cos2a=1-2*(-2/3)^2=1/9,
所以sin(2a-π/3)=sin2acosπ/3-cos2asinπ/3=±4√5/9*(1/2)-(1/9)*(√3/2)=±2√5/9-√3/18
y=f(x)=-sinx,因为f(a+π)=-sin(a+π)=sina=-2/3,则cosa=±√5/3,
sin2a=2*(-2/3)*(±√5/3)=±4√5/9,cos2a=1-2*(-2/3)^2=1/9,
所以sin(2a-π/3)=sin2acosπ/3-cos2asinπ/3=±4√5/9*(1/2)-(1/9)*(√3/2)=±2√5/9-√3/18