# PHP asin() Function

## Definition and Usage

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

For example, sin(pi/2)=1 and asin(1)=1.57079633 rad which is equal to pi/2.

This function returns a float value.

asin ( float $arg ) : float ## Parameters Sr.NoParameter & Description 1arg A floating point number whose arc sine is to be calculated. Number should be withing -1 to 1 ## Return Values PHP asin() function returns arc sine of given number. It is angle represented in radians. ## PHP Version This function is available in PHP versions 4.x, PHP 5.x as well as PHP 7.x. ## Example Live Demo Following example calculates asin(0.5) and returns 0.5235987755983 radians which is equivalent to pi/6 − <?php$arg=0.5;
$val=asin($arg);
echo "asin(" . $arg . ") = " .$val . " radians";
?>

## Output

This will produce following result −

asin(0.5) = 0.5235987755983 radians

## Example

Live Demo

Following example calculates asin(0) and returns 0 radians which is equivalent to sin(0) −

<?php
$arg=0;$val=asin($arg); echo "asin(" .$arg . ") = " . $val . " radians"; ?> ## Output This will produce following result − asin(0) = 0 radians ## Example Live Demo Let's check find out asin(-1). It returns -1.5707963267949 radians (which is -pi/2) − <?php$arg=-1;
$val=asin($arg);
echo "asin(" . $arg . ") = " .$val . " radians";
?>

## Output

This will produce following result −

asin(-1) = -1.5707963267949 radians

## Example

Live Demo

Following example returns NAN as the argument number is not within -1 to 1

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

## Output

This will produce following result −

asin(5) = NAN radians

Updated on: 29-Jun-2020

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