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sin(A-B)
=sinAcosB-cosAsinB
sinA+cosB=1/3
(sinA+cosB)^2=1/9
也就是sin^2A+cos^2B+2sinAcosB=1/9①
sinB-cosA=1/2
(sinB-cosA)^2=1/4
也就是sin^2B+cos^2A-2sinBcosA=1/4②
①+②得
sin^2A+cos^2B+2sinAcosB+sin^2B+cos^A-2sinBcosA=13/36
sin^2A+cos^2A+sin^2B+cos^2B+2sinAcosB-2sinBcosA=13/36
1+1+2(sinAcosB-cosAsinB)=13/36
2+2(sinAcosB-cosAsinB)=13/36
2(sinAcosB-cosAsinB)=-59/36
sinAcosB-cosAsinB=-59/72
=sinAcosB-cosAsinB
sinA+cosB=1/3
(sinA+cosB)^2=1/9
也就是sin^2A+cos^2B+2sinAcosB=1/9①
sinB-cosA=1/2
(sinB-cosA)^2=1/4
也就是sin^2B+cos^2A-2sinBcosA=1/4②
①+②得
sin^2A+cos^2B+2sinAcosB+sin^2B+cos^A-2sinBcosA=13/36
sin^2A+cos^2A+sin^2B+cos^2B+2sinAcosB-2sinBcosA=13/36
1+1+2(sinAcosB-cosAsinB)=13/36
2+2(sinAcosB-cosAsinB)=13/36
2(sinAcosB-cosAsinB)=-59/36
sinAcosB-cosAsinB=-59/72
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