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# acos(+Number, -Result)

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

Number
  A number.
Result
  Output: 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).
(24) number expected
  Number is not of a numeric type.
(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:
        Result is acos(1.0).	% gives Result = 0.0).
        Result is acos(-0.5).	% gives Result = 2.0944
        Result is acos(0).		% gives Result = 1.5708

    Error:
        Result is acos(2.0).	% arithmetic exception

## See Also

is / 2