Definition: The Greek letter "cos" represents circular arc in trigonometry, commonly used to find angle measures from a point on a unit circle (x-axis). The word "arccosine" is derived from the Latin 'arcus,' meaning "circle," and 'cosinus' which means cosine. It describes the angle that satisfies the equation:
\[ \cos(\theta) = \frac{x}{1+x^2} \]
For example, if a point on the unit circle at x=3 represents an angle of 60 degrees, then the corresponding arc from this point measures 180 degrees (60 degrees
π radians).
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