根据公式sin(a-b)=sinacosb-cosasinbsin(a-b)cosa-cos(a-b)sina 把（a-b）看成一项 逆着用上边的公式 有sin(a-b)cosa-cos(a-b)sina =sin(a-b-a)0.6 =sin(-b）所以sinb=-0.6cos2b=1-2(sinb)^2 =0.28...