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.

Syntax

asin ( float $arg ) : float

Parameters

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

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

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

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

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