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what is the inequality sign between cosx and x?

like sinx < x and x <tanx

2 Answers

Relevance
  • 5 years ago

    cos(x) = x at about x = 0.7390851332. Below that value,

    .. cos(x) > x

    Above that value

    .. cos(x) < x

    See the source link for a graph.

  • atsuo
    Lv 6
    5 years ago

    sin(x) < x < tan(x) for 0 < x < pi/2 .

    Let x = pi/2 - y .

    0 < pi/2 - y < pi/2

    -pi/2 < -y < 0

    0 < y < pi/2

    Thus

    sin(pi/2 - y) < pi/2 - y < tan(pi/2 - y) for 0 < y < pi/2

    cos(y) < pi/2 - y < cot(y)

    Swap y and x

    cos(x) < pi/2 - x < cot(x) for 0 < x < pi/2 ..... the answer

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