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222-9+11+12:2*14+14 = ? ( )

Toán Lớp 9: cho cos a=1/4.tìm tan a,cot a,sin a

Toán Lớp 9: cho cos a=1/4.tìm tan a,cot a,sin a

Comments ( 2 )

  1. Có: sin^2a+cos^2a=1
    <=> sin^2a+1/16=1
    <=> sin^2a=15/16
    <=> sina=+-\sqrt{15}/4
    -> tana=(sina)/(cosa)=(+-\sqrt{15}/4)/(1/4)=+-\sqrt{15}
    \qquad cota=1/(tana)=+-1/\sqrt{15}=+-\sqrt{15}/15
    Vậy sina=+-\sqrt{15}/4; tana=+-\sqrt{15}; cot a=+-\sqrt{15}/15

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222-9+11+12:2*14+14 = ? ( )