作业帮sin(a+b)=1/3,sin(a-b)=1/5,则tana*cotb=?
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sin(a+b)=1/3,sin(a-b)=1/5,则tana*cotb=?
sin(a+b)=1/3,sin(a-b)=1/5,则tana*cotb=?
sin(a+b)=1/3,sin(a-b)=1/5,则tana*cotb=?
sin(a+b)=sinαcosb+cosαsinb=1/3
sin(a-b)=sinαcosb-cosαsinb=1/5
俩个式子相加 sinαcosb+cosαsinb+sinαcosb-cosαsinb=2sinαcosb=8/15
俩个式子相减 sinαcosb+cosαsinb-sinαcosb+cosαsinb=2cosαsinb=2/15
得出 2sinαcosb=8/15,2cosαsinb=2/15
再相除 2sinαcosb/2cosαsinb=tana*cotb=4
两式展开,相加得一式,相减得一式
用两式相除
得tana*cotb=4
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