PHP asin() Function – Returns the Arcsine of a Value

The asin() function in PHP returns the arcsine of a given float argument, expressed in radians.

It is the inverse of sin(), meaning that for any value a within the function’s domain, a == sin(asin(a)).

Parameter: float $arg – the value to be processed.

Return value: The arcsine of $arg in radians.

Example usage:

<?php
echo asin(0.64);
echo asin(0);
echo asin(-1);
echo asin(1);
echo asin(2);
?>

Output:

0.694498265627
0
-1.57079632679
1.57079632679
-1.#IND