A=2Bsina,根据正弦定理得：sina=2sinbsina,Sinb=1/2.因为三角形是锐角三角形,所以b=30°,a+c=150°.cosa-sinc=cos(150°-c) -sinc=cos150°cosc+sin150°sinc-sinc=-√3/2 cosc+1/2 sinc-sinc=-√3/2 cosc-1/2 sinc=...