# Library Function atan in Math Class

## Library Function atan of math.h Header File in C

On this page we will discuss about library function atan in math class which is used in C.
The C header file math.h contains the standard math library functions that can be used for performing various mathematical operations. The atan function returns the arc tangent of x in radians. ## Library Function atan of math.h Header File

In C programming language the atan function is included in math.h header file.

The range of input argument which is passed to atan function is not limited here as it can be any value from negative to positive and returns the inverse tangent of parameter x in radians.

### Declaration of atan function

double atan(double x)


### Parameters of atan function

The atan function accepts a single input argument  which is a double value between -1 and 1.

ParameterDescription
double valueThis value of double function ranges from -1 to 1.

### Return value of atan function

The atan function returns a value in radians and it’s type is double. The function return value that lies in the range of $\left [ -\Pi/2,\Pi/2 \right ]$ radians.

ParameterReturn Value
$\left [ -\Pi/2,\Pi/2 \right ]$It returns the value in radians.

### Implementation of Library Function math.h atan

#### Example 1:

The following code shows the use of atan function.

Run
#include<stdio.h>
#include<conio.h>
#define PI 3.141592654
int main()
{
/* Define temporary variables */
double a, b, result;

/* Assign the two values to variables to find the atan2 of */
b = 4.56;
a = -12.5;

/* Calculate the Arc Tangent of value1 and value2 */
result = atan2(b, a);

/* Converting radians to degrees */
result = result * 180.0/PI;

/* Display the result of the calculation */
printf("The arc tangent of %.1lf and %.1lf is %.1lf degrees.", a, b, result);
return 0;
}


#### Output:

Inverse of tan(3.00) function = 1.25 in radians
Inverse of tan(3.00) function = 71.57 in degrees


#### Example 2:

Run

#include<stdio.h>
#define PI 3.141592654
int main()
{
double number = 9.0;
double return_value;
return_value = atan(number);
printf("Inverse of tan(%.3f) function = %.3f in radians", number, return_value);
return_value = (return_value * 180) / PI;
printf("\nInverse of tan(%.3f) function = %.3f in degrees", number, return_value);
return 0;
}


#### Output:

Inverse of tan(9.000) function = 1.460 in radians
Inverse of tan(9.000) function = 83.660 in degrees


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