已知α,β为锐角,且cosα=3/5,sin(α-β)=5/13,求cosβ的值.
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已知α,β为锐角,且cosα=3/5,sin(α-β)=5/13,求cosβ的值.
已知α,β为锐角,且cosα=3/5,sin(α-β)=5/13,求cosβ的值.
已知α,β为锐角,且cosα=3/5,sin(α-β)=5/13,求cosβ的值.
sin(α-β)=5/13,cos(α-β)=12/13,cosα=3/5,sinα=4/5
cosβ=cos[α-(α-β)]=cosαcos(α-β)+sinαsin(α-β)
=(3/5)(12/13)+(4/5)(5/13)
=56/65