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    Cos 9 Degrees

    Sin, Cos, Tan, Cot of an Angle
    Function
    Angle (°)

    What is cos 9°?

    Answer

    cos 9° ≈
    0.9877

    Angle in radians: 9° = π/20. The point of the angle is in quadrant I, where cosine is positive.

    ≈ — rounded to 4 decimal places. An exact form of cos 9° in square roots exists, but it is unwieldy — nested radicals.

    P(cos 9°, sin 9°) ≈ (0.9877, 0.1564)

    xyOP

    P(cos 9°, sin 9°) ≈ (0.9877, 0.1564)

    Highlighted: the projection on the x-axis — cosine, x ≈ 0.9877.

    All four functions of 9°
    FunctionExact valueDecimal
    sin 9°—≈ 0.1564
    cos 9°—≈ 0.9877
    tan 9°—≈ 0.1584
    cot 9°—≈ 6.3138

    See Also

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    <a href="https://calculat.io/en/number/trigonometry/cos--9">Cos 9 Degrees: Cosine of 9° on the Unit Circle - Calculatio</a>Copy
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    Cos 9 Degrees: Cosine of 9° on the Unit Circle. cos 9° ≈ 0.9877. The cosine is the x-coordinate of the point at 9° on the unit circle.
    https://calculat.io/en/number/trigonometry/cos--9/generated.jpgCopy

    Cosine of nearby angles

    Anglecos
    6°≈ 0.9945
    7°≈ 0.9925
    8°≈ 0.9903
    9°≈ 0.9877
    10°≈ 0.9848
    11°≈ 0.9816
    12°≈ 0.9781
    Recalculate with different values ↑

    FAQ

    What is cos 9°?

    cos 9° ≈ 0.9877

    Is there an exact value of cos 9°?

    Yes: 9° is a multiple of 3°, and the values of such angles can be written with square roots — but the expression is unwieldy, with nested radicals built from the values of 18° and 15° (3° = 18° − 15°). In practice the decimal is used: cos 9° ≈ 0.9877.

    Why does a calculator show −0.9111 for cos 9?

    The calculator is in radian mode (RAD): it takes cos 9 as the cosine of 9 radians, cos 9 rad ≈ −0.9111. Switch it to degrees (DEG): cos 9° ≈ 0.9877. In radians the value is never undefined: π is irrational, so a whole number of radians never lands exactly on an axis.

    See Also