<?php

// 21. octdec()

$num = "10";

echo octdec($num);

echo "\n";

// Output:

// 8

​

// 22. sin()

$num = pi() / 2;

echo sin($num);

echo "\n";

// Output:

// 1

​

// 23. cos()

$num = 0;

echo cos($num);

echo "\n";

// Output:

// 1

​

// 24. tan()

$num = pi() / 4;

echo tan($num);

echo "\n";

// Output:

// 1

​

// 25. asin()

$num = 1;

echo asin($num);

echo "\n";

// Output:

// 1.5707963267949 (approximately pi/2)

?>

​