Happy Coders

The acos() function in PHP returns the arc cosine (inverse cosine) of a number.
It accepts a float between -1 and 1 and returns the angle in radians.
This is useful in trigonometry to calculate angles when the cosine value is known.
The result will always be between 0 and π (0 to 3.14159…).
You can convert the result to degrees using rad2deg() if needed.

Syntax

acos(float $num): float

• $num: Must be between -1 and 1
• Returns the arc cosine of the number (in radians)

File Name: acos-example.php

<?php
echo acos(1);     // ➤ 0 radians
echo "\n";
echo acos(0);     // ➤ 1.5707963267949 (π/2)
echo "\n";
echo acos(-1);    // ➤ 3.1415926535898 (π)
?>

Convert Radians to Degrees

$angle = acos(0);              // π/2 radians
$degrees = rad2deg($angle);    // ➤ 90 degrees
echo $degrees;

Use Cases

• Trigonometry calculations
• Geometry (e.g., angle between vectors)
• Signal processing and physics formulas

Summary