# atan

function
```<cmath> ```
```     double atan (      double x );
float atan (       float x );
long double atan ( long double x );```

Compute arc tangent

Returns the principal value of the arc tangent of x, expressed in radians.

In trigonometrics, arc tangent is the inverse operation of tangent.

Notice that because of the sign ambiguity, a function cannot determine with certainty in which quadrant the angle falls only by its tangent value. You can use atan2 if you need to determine the quadrant.

In C++, this function is overloaded in <valarray> (see valarray atan).

### Parameters

x
Floating point value.

### Return Value

Principal arc tangent of x, in the interval [-pi/2,+pi/2] radians.

### Portability

In C, only the double version of this function exists with this name.

### Example

 1234567891011121314 ``````/* atan example */ #include #include #define PI 3.14159265 int main () { double param, result; param = 1.0; result = atan (param) * 180 / PI; printf ("The arc tangent of %lf is %lf degrees\n", param, result ); return 0; }``````

Output:
 ``` The arc tangent of 1.000000 is 45.000000 degrees. ```