# atan2

function

 Library: Trigonometry (OMTRIG legacy) Include: omtrig.xin Returns: Rectangular co-ordinates.

Declaration
```define external float function
atan2 (value float x, value float y)
```

Purpose

Use `atan2` with two rectangular co-ordinates, x and y, as arguments to calculate the arc tangent (y/x). `atan2` gives you the degree in radians. This trigonometric function works in conjunction with `hypot`.

In mathematics, the arc tangent is also called the inverse tangent.

Out-of-range values, such as acos() and asin() for |x| > 1, return "not a number" (NaN).

Example:

```  include "omtrig.xin"
process
local float x initial {1.1}
local float y initial {0.7}
local float atan2-value
set atan2-value to atan2 (x, y)
output "Take the rectangular co-ordinates x ( = "
|| "d" % x
|| " ) and y ( = "
|| "d" % y
|| " ) %n"
|| "Their arc tangent = "
|| "d" % atan2-value
|| "%n"
; Output: "Take the rectangular co-ordinates x ( = 1.1 ) and y ( = 0.7 )"
;          "Their arc tangent = 1.00406710927139"
```

Other Library Functions