已知α为第三象限角,且f(α)=sin(π-α)cos(2π-α)tan(-α+π)/sin(π+α)tan(2π-α)1)化简f(α) (2)cos(α-3π/2)=1/5,求f(α)的值 (3)若α=1920°,求f(α)的值
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![已知α为第三象限角,且f(α)=sin(π-α)cos(2π-α)tan(-α+π)/sin(π+α)tan(2π-α)1)化简f(α) (2)cos(α-3π/2)=1/5,求f(α)的值 (3)若α=1920°,求f(α)的值](/uploads/image/z/995090-50-0.jpg?t=%E5%B7%B2%E7%9F%A5%CE%B1%E4%B8%BA%E7%AC%AC%E4%B8%89%E8%B1%A1%E9%99%90%E8%A7%92%2C%E4%B8%94f%28%CE%B1%29%3Dsin%28%CF%80-%CE%B1%29cos%282%CF%80-%CE%B1%29tan%28-%CE%B1%2B%CF%80%29%2Fsin%28%CF%80%2B%CE%B1%29tan%282%CF%80-%CE%B1%291%EF%BC%89%E5%8C%96%E7%AE%80f%28%CE%B1%29+%EF%BC%882%EF%BC%89cos%EF%BC%88%CE%B1-3%CF%80%2F2%EF%BC%89%3D1%2F5%2C%E6%B1%82f%28%CE%B1%29%E7%9A%84%E5%80%BC+%EF%BC%883%EF%BC%89%E8%8B%A5%CE%B1%3D1920%C2%B0%2C%E6%B1%82f%28%CE%B1%29%E7%9A%84%E5%80%BC)
已知α为第三象限角,且f(α)=sin(π-α)cos(2π-α)tan(-α+π)/sin(π+α)tan(2π-α)1)化简f(α) (2)cos(α-3π/2)=1/5,求f(α)的值 (3)若α=1920°,求f(α)的值
已知α为第三象限角,且f(α)=sin(π-α)cos(2π-α)tan(-α+π)/sin(π+α)tan(2π-α)
1)化简f(α) (2)cos(α-3π/2)=1/5,求f(α)的值 (3)若α=1920°,求f(α)的值
已知α为第三象限角,且f(α)=sin(π-α)cos(2π-α)tan(-α+π)/sin(π+α)tan(2π-α)1)化简f(α) (2)cos(α-3π/2)=1/5,求f(α)的值 (3)若α=1920°,求f(α)的值
f(α)=sin(π-α)cos(2π-α)tan(-α+π)/sin(π+α)tan(2π-α)
=sinacosa(-tana)/(-sina)(-tana)
=-(sinacosatana/sinatana)
=cosa
cos(α-3π/2)=1/5
=cosacos3π/2+sinasin3π/2
=-sina=1/5
sina=-1/5
a在第三象限
cosa=负的五分之二倍根六
a=1920°
cos1920°=cos(11π-60°)=cos(π-60°)=-cos60°=-1/2
f(α)=sin(π-α)cos(2π-α)tan(-α+π)/sin(π+α)tan(2π-α)
=sinacosa(-tana)/(-sina)(-tana)
=-(sinacosatana/sinatana)
=-cosa
cos(α-3π/2)=1/5
cos(π/2+a-2π)=-sina=1/5
a第三象限,cosa=-2√6/5
1920-5*360=120
f(120)=-cos120=cos60=1/2