## XPath/XQuery tan function

### Summary

Returns the tangent of the argument. The argument is an angle in radians.

### Signature

`math:tan`(
`\$θ` as `xs:double?`
) as `xs:double?`

### Properties

This function is deterministic, context-independent, and focus-independent.

### Rules

If `\$` θ is the empty sequence, the function returns the empty sequence.

Otherwise the result is the tangent of `\$` θ (which is treated as an angle in radians) as defined in the specification of the `tan` function applied to 64-bit binary floating point values.

### Examples

The expression `math:tan(())` returns `()`.

The expression `math:tan(0)` returns `0.0e0`.

The expression `math:tan(-0.0e0)` returns `-0.0e0`.

The expression `math:tan(math:pi() div 4)` returns `1.0e0`.

The expression `math:tan(-math:pi() div 4)` returns `-1.0e0`.

The expression `1 div math:tan(math:pi() div 2)` returns `0.0e0`.

The expression `1 div math:tan(-math:pi() div 2)` returns `-0.0e0`.

The expression `math:tan(math:pi())` returns `0.0e0`.

The expression `math:tan(xs:double('NaN'))` returns `xs:double('NaN')`.

The expression `math:tan(xs:double('INF'))` returns `xs:double('NaN')`.

The expression `math:tan(xs:double('-INF'))` returns `xs:double('NaN')`.

### Notes

The treatment of the `invalidOperation` and `underflow` exceptions is defined in .

If `\$` θ is positive or negative infinity, or `NaN`, then the result is `NaN`.