acos(): the arc cosine (inverse cosine) of a given number in radians

<?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 
?>

acos(X);

deg2rad() with acos()

<?Php
echo acos(deg2rad(0)); // 1.5707963267949
echo "<br>";
echo acos(deg2rad(90)); // NAN
echo "<br>";
echo acos(deg2rad(180)); // NAN 
?>

Example: Handling Out-of-Range Values

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

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

78.463040967185

Questions