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The acosh() function in PHP returns the inverse hyperbolic cosine of a number.
It accepts a float value greater than or equal to 1 and returns the result in radians.
This function is useful in engineering, physics, and complex math operations.
It essentially reverses the effect of the cosh() function.
If the input is less than 1, the function will return NAN (Not a Number).

Syntax

acosh(float $number): float

• • Parameter:
    number must be greater than or equal to 1
  • Returns:
    The inverse hyperbolic cosine of the given number (in radians)

File Name: acosh-example.php

<?php
echo acosh(1);     // ➤ 0
echo "\n";
echo acosh(2);     // ➤ 1.3169578969248
echo "\n";
echo acosh(10);    // ➤ 2.9932228461264
?>

Formula (Internal Logic)

Mathematically:

acosh(x) = log(x + sqrt(x² - 1))

Use Cases