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The cosine of an angle , denoted as , is one of the most important [circular] trigonometric functions.

Given the angle of an arc on a unit circle, is the length of the side on a right triangle going along a line along (the other two sides being a side opposing a vertex coinciding with the center of the circle and hypotenuse).


Per the Pythagorean theorem, .

The following graph shows the sine and cosine functions graphed together (sine is in red, cosine in blue):

Sin Cos Graph.png

Taylor series expansion

The Taylor series expansion of the cosine function is



See also


  1. Provide illustration.