Question

在△ABC中 角A B C所对边分别为abc 已知cosC+cos(A-B)=1/3且3tanAtanB=1

Answer 1

1、cosC=cos(180-A-B)=-cos(A+B)cosC+cos(A-B)=cos(A-B)-cos(A+B)=cosAcosB+sinAsinB-cosAcosB+sinAsinB=2sinAsinB=1/3 3tanAtanB=1所以cosAcosB=1/22、向量a·向量b=ab(cosAcosB+sinAsinB)=ab(1/6+1/2)=2ab/3S=0.5a...