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    Cos 21 Degrees

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

    What is cos 21°?

    Answer

    cos 21° ≈
    0.9336

    Angle in radians: 21° = 7π/60. The point of the angle is in quadrant I, where cosine is positive.

    ≈ — rounded to 4 decimal places. An exact form of cos 21° in square roots exists, but it is unwieldy — nested radicals.

    P(cos 21°, sin 21°) ≈ (0.9336, 0.3584)

    xyOP

    P(cos 21°, sin 21°) ≈ (0.9336, 0.3584)

    Highlighted: the projection on the x-axis — cosine, x ≈ 0.9336.

    All four functions of 21°
    FunctionExact valueDecimal
    sin 21°—≈ 0.3584
    cos 21°—≈ 0.9336
    tan 21°—≈ 0.3839
    cot 21°—≈ 2.6051

    See Also

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    https://calculat.io/en/number/trigonometry/cos--21Copy
    <a href="https://calculat.io/en/number/trigonometry/cos--21">Cos 21 Degrees: Cosine of 21° on the Unit Circle</a>Copy
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    Cos 21 Degrees: Cosine of 21° on the Unit Circle. cos 21° ≈ 0.9336. The cosine is the x-coordinate of the point at 21° on the unit circle.
    https://calculat.io/en/number/trigonometry/cos--21/generated.jpgCopy

    Cosine of nearby angles

    Anglecos
    18°√(10 + 2√5)/4
    19°≈ 0.9455
    20°≈ 0.9397
    21°≈ 0.9336
    22°≈ 0.9272
    23°≈ 0.9205
    24°≈ 0.9135
    Recalculate with different values ↑

    FAQ

    What is cos 21°?

    cos 21° ≈ 0.9336

    Is there an exact value of cos 21°?

    Yes: 21° 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 21° ≈ 0.9336.

    Why does a calculator show −0.5477 for cos 21?

    The calculator is in radian mode (RAD): it takes cos 21 as the cosine of 21 radians, cos 21 rad ≈ −0.5477. Switch it to degrees (DEG): cos 21° ≈ 0.9336. In radians the value is never undefined: π is irrational, so a whole number of radians never lands exactly on an axis.

    See Also