3(sinA)^2+2(sinB)^2=1→cos2B=3(sinA)^23sin2A-2sin2B=0 →sin2B=3sin2A/2cos(A+2B)=cosAcos2B-sinAsin2B=3cosA(sinA)^2-3sinAsin2A/2=0→A+2B=90 参考:2sin^2 b=1-cos2b ∴3sin^2 a=cos2b 3sin2a-2sin2b → sin2b=...