cosa=5/13,cos(a+b)=-4/5,求cosb=求出sina=12/13.sina(a+b)=-3/5cos(a+b)=cosacosb-sinasinb=-4/5代入缺少两个条件:sinb,cosb怎么求
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![cosa=5/13,cos(a+b)=-4/5,求cosb=求出sina=12/13.sina(a+b)=-3/5cos(a+b)=cosacosb-sinasinb=-4/5代入缺少两个条件:sinb,cosb怎么求](/uploads/image/z/1801873-1-3.jpg?t=cosa%3D5%2F13%2Ccos%28a%2Bb%29%3D-4%2F5%2C%E6%B1%82cosb%3D%E6%B1%82%E5%87%BAsina%3D12%2F13.sina%28a%2Bb%29%3D-3%2F5cos%28a%2Bb%29%3Dcosacosb-sinasinb%3D-4%2F5%E4%BB%A3%E5%85%A5%E7%BC%BA%E5%B0%91%E4%B8%A4%E4%B8%AA%E6%9D%A1%E4%BB%B6%3Asinb%2Ccosb%E6%80%8E%E4%B9%88%E6%B1%82)
cosa=5/13,cos(a+b)=-4/5,求cosb=求出sina=12/13.sina(a+b)=-3/5cos(a+b)=cosacosb-sinasinb=-4/5代入缺少两个条件:sinb,cosb怎么求
cosa=5/13,cos(a+b)=-4/5,求cosb=
求出sina=12/13.
sina(a+b)=-3/5
cos(a+b)=cosacosb-sinasinb=-4/5
代入缺少两个条件:sinb,cosb
怎么求
cosa=5/13,cos(a+b)=-4/5,求cosb=求出sina=12/13.sina(a+b)=-3/5cos(a+b)=cosacosb-sinasinb=-4/5代入缺少两个条件:sinb,cosb怎么求
cosb=cos(a+b-a)
=cos(a+b)*cosa+sin(a+b)*sina
=5/13*(-4/5)+(-3/5)*12/13
=56/65