Inverse Cosine Calculator (arccos)
Find arccos(x), the angle whose cosine is x, in degrees and radians.
Change the values and press Calculate to work out your own figures.
Enter the value x.
Show the working
- The principal value lies in 0° to 180°
- arccos(0.5) = 1.047197551 rad = 60°
How to use it
Enter the value x.
Enter the values you know (decimals, fractions, surds such as 2√5, or angles such as π/3 in radians). Show the working gives the rule used at each step.
Key facts
arccos(x) is the angle in [0°, 180°] whose cosine is x
Principal value
Many angles share a cosine; the inverse returns the one in the principal range, and the others differ by whole turns (or reflections).
Questions
What is arccos(0.5)?
60° (π/3).
What values are allowed?
Any number for arctangent; −1 to 1 for arcsine and arccosine.
Formulas
arccos(x) is the angle in [0°, 180°] whose cosine is x
Sources
Limitations
- Angles can be typed in degrees or radians; radians may be written with π (π/3, 2pi/3).