# PHP acos() Function

PHPServer Side ProgrammingProgramming

## Definition and Usage

The acos() function Returns the arc cosine or cos inverse of arg in radians. acos() is the inverse function of cos(). Therefore if cos(x)=y, acos(y)=x.

For example, cos(pi/2)=0 and acos(0)=1.57079633 rad which is equal to pi/2.

This function returns a float value.

acos ( float $arg ) : float ## Parameters Sr.NoParameter & Description 1arg A floating point number whose arc cosine is to be calculated. Number should be withing -1 to 1 ## Return Values PHP acos() function returns arc cosine of given number. It is angle represented in radians. ## PHP Version This function is available in PHP versions 4.x, PHP 5.x as well as PHP 7.x. ## Example Live Demo Following example calculates acos(0.5) and returns 1.04719755 radians which is equivalent to pi/3 − <?php$arg=0.5;
$val=acos($arg);
echo "acos(" . $arg . ") = " .$val . " radians";
?>

## Output

This will produce the following result −

acos(0.5) = 1.0471975511966 radians

## Example

Live Demo

Following example calculates acos(0) and returns 1.5707963267949 radians which is equivalent to pi/2 −

<?php
$arg=0;$val=acos($arg); echo "acos(" .$arg . ") = " . $val . " radians"; ?> ## Output This will produce the following result − acos(0) = 1.5707963267949 radians ## Example Live Demo Let's check find out acos(-1). It returns 3.14159265 radians (which is pi) − <?php$arg=-1;
$val=acos($arg);
echo "acos(" . $arg . ") = " .$val . " radians";
?>

## Output

This will produce the following result −

acos(-1) = 3.1415926535898 radians

## Example

Live Demo

The following example returns NAN as the argument number is not within -1 to 1.

<?php
$arg=5;$val=acos($arg); echo "acos(" .$arg . ") = " . \$val . " radians";
?>

## Output

This will produce the following result −

acos(5) = NAN radians