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# tan(+Number, -Result)

Evaluates the trigonometric function tan(Number) and unifies the resulting
value with Result.
*Number*
- A number.
*Result*
- Output: float or breal.

## Description

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

which should be preferred for portability.
In coroutining mode, if Number is uninstantiated, the call to tan/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 (2k +1) * pi/2 for every integer k.

## Examples

Success:
Result is tan(0). % gives Result = 0.0
Result is tan(12.3). % gives Result = -0.272854
Result is tan(-1). % gives Result = -1.55741
Error:
X is pi/2, tan(X). % arithmetic exception

## See Also

is / 2