∵C-A=π/2,A+B+C=π,
∴2A=π/2-B
则cos(2A)=cos(π/2-B)=sinB=1/3
即1-2（sinA)^2=1/3
(sinA)^2=1/3
∵C=A+π/2＞π/2,0＜A＜π/2,∴sinA＞0
∴sinA=√3/3