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## arc cosine function

The `acos` function is an inverse trigonometric function. The `acos` function returns the arc cosine (inverse of cosine) of the input expression.

Syntax:

    double acos(n)

Semantics:

- n: The argument n is an expression that resolves to a number.
- return type: double.

  The resultant angle is expressed in radians and is in the range 0.0 through `pi` with the following exceptions:

  - Returns a NULL value in the following cases:
    - n resolves to a NULL value
    - n does not resolve to a number
  - Returns NaN in the following cases:
    - n resolves to NaN
    - absolute value of n is greater than one
    - n resolves to positive/negative infinity

Example 12-72 arc cosine function

    SELECT acos(n) FROM Archery

Value of n | Output
--- | ---
1 | 0.0
0 | 1.5707963267948966
sqrt(3)/2 | 0.5235987755982989
0.5 | 1.0471975511965979
-1 | 3.141592653589793