Sin 81 Degrees
Sin, Cos, Tan, Cot of an Angle
What is sin 81°?
Answer
sin 81° ≈
0.9877
Angle in radians: 81° = 9π/20. The point of the angle is in quadrant I, where sine is positive.
≈ — rounded to 4 decimal places. An exact form of sin 81° in square roots exists, but it is unwieldy — nested radicals.
P(cos 81°, sin 81°) ≈ (0.1564, 0.9877)
P(cos 81°, sin 81°) ≈ (0.1564, 0.9877)
Highlighted: the projection on the y-axis — sine, y ≈ 0.9877.
See Also
- Arcsin, Arccos, Arctan, Arccot - The angle from the value of its sine, cosine, tangent or cotangent: exact in degrees and π, with the check and the unit circle
- Square Root Calculator - Calculate the square root of any number
- Simplify Square Root Calculator - Write any square root in simplest radical form, step by step
- Geometry Formulas: Area, Volume, Perimeter - The formula for every standard shape, where it comes from, and worked examples
Sine of nearby angles
FAQ
What is sin 81°?
sin 81° ≈ 0.9877
Is there an exact value of sin 81°?
Yes: 81° 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 81° ≈ 0.9877.
Why does a calculator show −0.6299 for sin 81?
The calculator is in radian mode (RAD): it takes sin 81 as the sine of 81 radians, sin 81 rad ≈ −0.6299. Switch it to degrees (DEG): sin 81° ≈ 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
- Sin 71 Degrees: Sine of 71° on the Unit Circle
- Sin 72 Degrees: Sine of 72° on the Unit Circle
- Sin 73 Degrees: Sine of 73° on the Unit Circle
- Sin 74 Degrees: Sine of 74° on the Unit Circle
- Sin 75 Degrees: Sine of 75° on the Unit Circle
- Sin 76 Degrees: Sine of 76° on the Unit Circle
- Sin 77 Degrees: Sine of 77° on the Unit Circle
- Sin 78 Degrees: Sine of 78° on the Unit Circle
- Sin 79 Degrees: Sine of 79° on the Unit Circle
- Sin 80 Degrees: Sine of 80° on the Unit Circle
- Sin 82 Degrees: Sine of 82° on the Unit Circle
- Sin 83 Degrees: Sine of 83° on the Unit Circle
- Sin 84 Degrees: Sine of 84° on the Unit Circle
- Sin 85 Degrees: Sine of 85° on the Unit Circle
- Sin 86 Degrees: Sine of 86° on the Unit Circle
- Sin 87 Degrees: Sine of 87° on the Unit Circle
- Sin 88 Degrees: Sine of 88° on the Unit Circle
- Sin 89 Degrees: Sine of 89° on the Unit Circle
- Sin 90 Degrees: Sine of 90° on the Unit Circle
- Sin 97 Degrees: Sine of 97° on the Unit Circle
- Синус 81 градуса (sin 81°) на единичной окружности
- Seno de 81 grados (sen 81°) en el círculo unitario
- Seno de 81 graus (sen 81°) no ciclo trigonométrico