在三角形ABC中,sin(A+B)+sin(A-B)=根號6/2,cos(A+B)+cos(A-B)=-根號2/2,則B= 求過程!

在三角形ABC中,sin(A+B)+sin(A-B)=根號6/2,cos(A+B)+cos(A-B)=-根號2/2,則B= 求過程!

sin(A+B)+sin(A-B)=sinAcosB+cosAsinB+sinAcosB-cosAsinB=√6/22sinAcosB=√6/2sinAcosB=√6/4……①cos(A+B)+cos(A-B)=cosAcosB-sinAsinB+cosAcosB+sinAsinB=-√2/22cosAcosB=-√2/2cosAcosB=-√2/4……②①/②式…