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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

### 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