Cos 126 Degrees
Sin, Cos, Tan, Cot of an Angle
What is cos 126°?
Answer
cos 126° =
−√(10 − 2√5)/4 ≈ −0.5878
Angle in radians: 126° = 7π/10. The point of the angle is in quadrant II, where cosine is negative.
≈ — rounded to 4 decimal places.
cos 126° = cos(180° − 54°) = −cos 54° = −√(10 − 2√5)/4
P(cos 126°, sin 126°) = (−√(10 − 2√5)/4, (√5 + 1)/4)
Regular pentagon (golden ratio): cos 36° = (√5 + 1)/4.
cos 54° = sin 36° = √(1 − cos² 36°) = √(10 − 2√5)/4
P(cos 126°, sin 126°) ≈ (−0.5878, 0.8090)
Highlighted: the projection on the x-axis — cosine, x ≈ −0.5878.
| Function | Exact value | Decimal |
|---|---|---|
| sin 126° | (√5 + 1)/4 | ≈ 0.8090 |
| cos 126° | −√(10 − 2√5)/4 | ≈ −0.5878 |
| tan 126° | −√(25 + 10√5)/5 | ≈ −1.3764 |
| cot 126° | −√(5 − 2√5) | ≈ −0.7265 |
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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
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