10. （2023春•吴江区校级月考）已知sin(15∘−α2)=33\sin (15\circ -\frac{\alpha }{2})=\frac{\sqrt{3}}{3}sin(15∘−2α)=33，则cos(30∘−α)=(\cos (30\circ -\alpha )=(cos(30∘−α)=( )))