1－cos(A+B)+cos2C=1cos2C=cos(A+B)=-cosC=2cosC^2-1解得cosC=-1(舍)或1/2,所以sinC=√3/2a^2=b^2+0.5c^2=b^2+c^2-2bccosC所以0.5c^2=c^2-2bccosC所以b=0.5c因为b/sinB=c/sinC所以sinB=√3/4若cosB＝－√13/4则B+C>...