sekibunn.php

<?php
// https://paiza.io/projects/szvtfJnxiwMhun_ndDxs6w

$a = [4,8,16,32,64,900];
for($i=0;$i<count($a);$i++){
    $h = 1 / $a[$i];
    $y0 = y(0);
    $yn = y(1);
    $x = 0;
    $y = 0;
    for($j=0;$j<$a[$i] - 2;$j++){
        $x += $h;
        $y += y($x);
    }
    echo "n=", $a[$i], "I=" , ($h / 2)*($y0+$yn+2*$y);
    echo PHP_EOL;    
}


function y($x){
    return (1 / (1 + $x**2));
}
?>