由已知2/sin60º=2R即2R=4/(√3)；A+C=120º ,∴ 又a=2RsinA ;c=2RsinC∴面积S=1/2·acsinB=1/2·4R²sinAsinCsin60º=(4√3)/3·sinAsinC=(4√3)/3·(-1/2)[cos(A+C)-cos(A-C)]=(4√3)/3·(-1/2)[c...