(1)cosB=cos(B-π/4+π/4)=cos(B-π/4)cos(π/4)-sin(B-π/4)sin(π/4)=【（√2）/2】*（1/3-2√2/3）=（√2-4）/6,sinB^2=1-cosB^2===>sinB=（√2+4）/6,
sin2B=2sinBcosB=2*（√2-4）/6*（√2+4）/6=-7/9
(2)同样sina=sin(a+B-B),自己试试看.