Math Trigonometric functions acos() to get acos value of any radian as input in PHP

Calculate inverse cosine

acos() accepts a value from -1 through 1 and returns the corresponding angle in radians.

$angle = acos(0.5);
echo rad2deg($angle); // approximately 60

The examples below build from the basic call to practical variations and edge cases.

<?Php
echo acos(0); // Output is 1.5707963267949
echo "<br>";
echo acos(1); // Output  0
echo "<br>";
echo acos(-1); // Output is 3.1415926535898
echo "<br>";
echo acos(-5); // Output is NAN 
?>

Syntax

acos(float $num): float;

The argument is a cosine value, not an angle. Valid real inputs are from -1 through 1. Values outside that range return NAN. Use is_nan() to test the result.

Convert the returned angle to degrees

acos() returns radians. Use rad2deg() when the result needs to be displayed in degrees.

$cosine = 0.5;
$angleRadians = acos($cosine);
echo rad2deg($angleRadians); // 60

Example: Handling Out-of-Range Values

$value = 2;  // Out of range
$result = acos($value);
if (is_nan($result)) {
    echo "Invalid input for acos";
}

Output

Invalid input for acos

Example: Calculating Angles in a Triangle Using Law of Cosines

$a = 5; $b = 6; $c = 7;
$angleC = acos(($a*$a + $b*$b - $c*$c) / (2 * $a * $b));
echo rad2deg($angleC);  // Output in degrees

Output

78.463040967185

Questions

What does the `acos()` function in PHP do?
What is the purpose of the `acos()` function in PHP?
How is the `acos()` function used to calculate the inverse cosine of a number?
What is the range of values returned by the `acos()` function in PHP?
Can the `acos()` function be used with both degrees and radians?
What happens if you pass an invalid argument to the `acos()` function?
How can you use the `acos()` function to calculate the angle in radians given the cosine value?
Are there any alternative ways to calculate the inverse cosine in PHP besides using the `acos()` function?
Can the `acos()` function return a complex number?
What type of value does the `acos()` function return: integer, float, or something else?

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Subhendu Mohapatra

Author & Instructor at plus2net

I write and maintain practical tutorials on Python, PHP, SQL, JavaScript, HTML, jQuery, and web development at plus2net. The tutorials focus on clear explanations, working examples, and code that readers can test and adapt while learning.

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acos(): inverse cosine of a value from -1 to 1