已知cos(a-B/2)=-1/9,sin(a/2-B)=2/3,且π/2

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已知cos(a-B/2)=-1/9,sin(a/2-B)=2/3,且π/2已知cos(a-B/2)=-1/9,sin(a/2-B)=2/3,且π/2已知cos(a-B/2)=-1/9,sin(a/2-

已知cos(a-B/2)=-1/9,sin(a/2-B)=2/3,且π/2
已知cos(a-B/2)=-1/9,sin(a/2-B)=2/3,且π/2

已知cos(a-B/2)=-1/9,sin(a/2-B)=2/3,且π/2
∵π/2

π/4所以：sin(a-B/2)=4√5/9 ，cos(a/2-B)=√5/3
cos[(a-B/2)-(a/2-B)]=cos[(a+b)/2]=cos(a-B/2)cos(a/2-B)+sin(a-B/2)sins(a/2-B)=-1/9 * √5/3+
4√5/9 * 2/3=7√5/27
cos(a+B)=2cos[(a+b)/2]^2-1=-239/729