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# acos(+Number, -Result)

Evaluates the trigonometric function acos(Number) and unifies the resulting value with Result.

Number
  A number.
Result
  A variable or float.

## Description

This predicate is used by the ECLiPSe compiler to expand evaluable arithmetic expressions. So the call to acos(Number, Result) is equivalent to

        Result is acos(Number)

which should be preferred for portability.

In coroutining mode, if Number is uninstantiated, the call to acos/2 is delayed until this variable is instantiated.

### Modes and Determinism

- acos(+, -) is det

### Exceptions

(4) instantiation fault
  Number is not instantiated (non-coroutining mode only).
(5) type error
  Result is a number but not a float
(24) number expected
  Number is not of a numeric type.
(24) number expected
  Result is neither a number nor a variable.
(20) arithmetic exception
  Illegal arithmetic operation: Number is greater than 1 or less than -1.
(141) unimplemented functionality
  Argument is of type breal

## Examples

    Success:
          acos(1.0, 0.0).
          acos(-0.5, Result).       (gives Result = 2.0944)
          acos(0, Result).          (gives Result = 1.5708)
    Fail:
          acos(1, 1.0).
    Error:
          acos(A, 6.0).             (Error 4).
          acos(1, r).               (Error 5).
          acos(1, 0).               (Error 5).
          acos(2, Result).          (Error 20).
          acos(4 - 3, 0.0).         (Error 24).

## See Also

is / 2