Sin 21 Degrees

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

What is sin 21°?

Answer

sin 21° ≈
0.3584

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

≈ — rounded to 4 decimal places. An exact form of sin 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 y-axis — sine, y ≈ 0.3584.

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

Recalculate with different values ↑

Sine of nearby angles

Anglesin
18°(√5 − 1)/4
19°≈ 0.3256
20°≈ 0.3420
21°≈ 0.3584
22°≈ 0.3746
23°≈ 0.3907
24°≈ 0.4067

FAQ

What is sin 21°?

sin 21° ≈ 0.3584

Is there an exact value of sin 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: sin 21° ≈ 0.3584.

Why does a calculator show 0.8367 for sin 21?

The calculator is in radian mode (RAD): it takes sin 21 as the sine of 21 radians, sin 21 rad ≈ 0.8367. Switch it to degrees (DEG): sin 21° ≈ 0.3584. In radians the value is never undefined: π is irrational, so a whole number of radians never lands exactly on an axis.

See Also