# PHP atan() Function

## Definition and Usage

The atan() function returns the arc tan or tan inverse of arg in radians. atan() is the inverse function of tan(). Therefore if tan(x)=y, atan(y)=x.

For example, tan(pi/3)= 1.73205080757 (Squre Root of 3) and atan(1.73205080757)=1.04719755 rad which is equal to pi/3.

This function returns a float value .

atan ( float $arg ) : float ## Parameters Sr.NoParameter & Description 1arg A floating point number whose arc tan is to be calculated. ## Return Values PHP atan() function returns arc tan of given number. It is angle represented in radians. Returned value is between -pi/2 and pi/2 ## PHP Version This function is available in PHP versions 4.x, PHP 5.x as well as PHP 7.x. ## Example Live Demo Following example calculates atan(0.57735026919) and returns 0.52359877559858 radians which is equivalent to pi/6. Note that tan(pi/6) is 1/sqrt(3) − <?php$arg=0.57735026919;
$val=atan($arg);
echo "atan(" . $arg . ") = " .$val . " radians";
?>

## Output

This will produce following result −

atan(0.57735026919) = 0.52359877559858 radians

## Example

Live Demo

Following example calculates atan(0) and returns 0 radians which is equivalent to tan(0) −

<?php
$arg=0;$val=atan($arg); echo "atan(" .$arg . ") = " . $val . " radians"; ?> ## Output This will produce following result − atan(0) = 0 radians ## Example Live Demo Let's check find out atan(-1). It returns -0.78539816339745 radians (which is -pi/4) − <?php$arg=-1;
$val=atan($arg);
echo "atan(" . $arg . ") = " .$val . " radians";
?>

## Output

This will produce following result −

atan(-1) = -0.78539816339745 radians

## Example

Live Demo

Following example calculates atan(1.6331239E+16) which is a very large number and returns 1.5707963267949 radians which is equivalent to pi/2 −

<?php
$arg=1.6331239e+16;$val=atan($arg); echo "atan(" .$arg . ") = " . \$val . " radians";
?>

## Output

This will produce following result −

atan(1.6331239E+16) = 1.5707963267949 radians