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    Cos 66 Degrees

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

    What is cos 66°?

    Answer

    cos 66° ≈
    0.4067

    Angle in radians: 66° = 11π/30. The point of the angle is in quadrant I, where cosine is positive.

    ≈ — rounded to 4 decimal places. An exact form of cos 66° in square roots exists, but it is unwieldy — nested radicals.

    P(cos 66°, sin 66°) ≈ (0.4067, 0.9135)

    xyOP

    P(cos 66°, sin 66°) ≈ (0.4067, 0.9135)

    Highlighted: the projection on the x-axis — cosine, x ≈ 0.4067.

    All four functions of 66°
    FunctionExact valueDecimal
    sin 66°—≈ 0.9135
    cos 66°—≈ 0.4067
    tan 66°—≈ 2.2460
    cot 66°—≈ 0.4452

    See Also

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    https://calculat.io/en/number/trigonometry/cos--66Copy
    <a href="https://calculat.io/en/number/trigonometry/cos--66">Cos 66 Degrees: Cosine of 66° on the Unit Circle</a>Copy
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    Cos 66 Degrees: Cosine of 66° on the Unit Circle. cos 66° ≈ 0.4067. The cosine is the x-coordinate of the point at 66° on the unit circle.
    https://calculat.io/en/number/trigonometry/cos--66/generated.jpgCopy

    Cosine of nearby angles

    Anglecos
    63°≈ 0.4540
    64°≈ 0.4384
    65°≈ 0.4226
    66°≈ 0.4067
    67°≈ 0.3907
    68°≈ 0.3746
    69°≈ 0.3584
    Recalculate with different values ↑

    FAQ

    What is cos 66°?

    cos 66° ≈ 0.4067

    Is there an exact value of cos 66°?

    Yes: 66° 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 66° ≈ 0.4067.

    Why does a calculator show −0.9996 for cos 66?

    The calculator is in radian mode (RAD): it takes cos 66 as the cosine of 66 radians, cos 66 rad ≈ −0.9996. Switch it to degrees (DEG): cos 66° ≈ 0.4067. In radians the value is never undefined: π is irrational, so a whole number of radians never lands exactly on an axis.

    See Also