( 1)、a/sinA = b/sinB = b/sin2A = b/2 sinA cosa，

——》cosA=b/2a=2√6/6=√6/3，

(2)、sinA=√( 1-cosA^2)=√3/3，

——《sinB = 2 Sina cosa = 2√2/3，

cosb=cos2a= 1-2sin^2a= 1/3，

——《cosC =-cos(A+B)= Sina sinb-cosAcosB =√6/9，

——”C = arccos√6/9 .