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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

### 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