sinA+sinB=1/2,cosA+cosB=-2/3,求:tanA*tanB=?
问题描述:
sinA+sinB=1/2,cosA+cosB=-2/3,求:tanA*tanB=?
答
(sinA+sinB)^2=1/4……(1)(cosA+cosB)^2=4/9……(2)(1)+(2),整理得2+2(sinAsinB+cosAcosB)=25/36sinAsinB+cosAcosB=-47/72cos(A-B)=-47/72……(3)sin(A-B)=±√{1-[cos(A-B)]^2}(2)-(1),整理得cos...