α为第三象限角 f(α)=Sin(π+αCos(2π-α)/tan(π-α)Sin3/2π-α) 1、化简f(α)2、若Cos(α-3/2π)=1/5 3、α=-1380°,求f(α)
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![α为第三象限角 f(α)=Sin(π+αCos(2π-α)/tan(π-α)Sin3/2π-α) 1、化简f(α)2、若Cos(α-3/2π)=1/5 3、α=-1380°,求f(α)](/uploads/image/z/5939277-69-7.jpg?t=%CE%B1%E4%B8%BA%E7%AC%AC%E4%B8%89%E8%B1%A1%E9%99%90%E8%A7%92+f%28%CE%B1%29%3DSin%28%CF%80%2B%CE%B1Cos%282%CF%80-%CE%B1%29%2Ftan%28%CF%80-%CE%B1%29Sin3%2F2%CF%80-%CE%B1%29+1%E3%80%81%E5%8C%96%E7%AE%80f%28%CE%B1%EF%BC%892%E3%80%81%E8%8B%A5Cos%28%CE%B1-3%2F2%CF%80%29%3D1%2F5+3%E3%80%81%CE%B1%3D-1380%C2%B0%2C%E6%B1%82f%28%CE%B1%29)
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α为第三象限角 f(α)=Sin(π+αCos(2π-α)/tan(π-α)Sin3/2π-α) 1、化简f(α)2、若Cos(α-3/2π)=1/5 3、α=-1380°,求f(α)
α为第三象限角 f(α)=Sin(π+αCos(2π-α)/tan(π-α)Sin3/2π-α) 1、化简f(α)2、若Cos(α-3/2π)=1/5 3、α=-1380°,求f(α)
α为第三象限角 f(α)=Sin(π+αCos(2π-α)/tan(π-α)Sin3/2π-α) 1、化简f(α)2、若Cos(α-3/2π)=1/5 3、α=-1380°,求f(α)
是Sin(π+α)Cos(2π-α)/tan(π-α)Sin3/2π-α)
1、
Sin(π+α) = -Sinα
Cos(2π-α) = Cosα
tan(π-α) = -tanα =-sinα/cosα
Sin3/2π-α) = -cosα
∴ f(α)= - cosα
2、
Cos(α-3/2π)=1/5 = -Sinα
由cos^2 α +sin^2 α =1得
cos α = -2√6 /5
f(α)= - cosα = 2√6 /5
3、
α=-1380°
f(α)= - cosα =-cos1380 ° = -cos60° =-1/2