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For the exact argument  , Mathematica returns an exact result.
For a machine‐number argument (a numerical argument with a decimal point and not too many digits), a machine number is also returned.
The next inputs calculate 100‐digit approximations at  and  .
Within a second, it is possible to calculate thousands of digits for the cosine function. The next input calculates 10000 digits for  and analyzes the frequency of the digit  in the resulting decimal number.
Here is a 50‐digit approximation of the cosine function at the complex argument  .
Mathematica automatically evaluates mathematical functions with machine precision, if the arguments of the function are machine‐number elements. In this case, only six digits after the decimal point are shown in the results. The remaining digits are suppressed, but can be displayed using the function InputForm.
Mathematica knows the symmetry and periodicity of the cosine function. Here are some examples:
Mathematica automatically simplifies the composition of the direct and the inverse cosine functions into its argument.
Mathematica also automatically simplifies the composition of the direct and any of the inverse trigonometric functions into algebraic functions of the argument.
If the argument has the structure  or  , and  or  with integer  , the cosine function can be automatically transformed into trigonometric or hyperbolic sine or cosine functions.
Sometimes simple arithmetic operations containing the cosine function can automatically produce other trigonometric functions.
The cosine function can be treated as a particular case of some more general special functions. For example,  can appear automatically from Bessel, Mathieu, Jacobi, hypergeometric, and Meijer functions for appropriate values of their parameters.
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