function cubeRoot($n) {
if ($n >= 0)
return pow($n, (double) 1 / 3);
else
return -pow((-$n), (double) 1 / 3);
}
$n = 27;
echo cubeRoot($n) . "\n";
echo cubeRoot(16) . "\n";
echo cubeRoot(-27) . "\n";
echo cubeRoot(64) . "\n";
/*
run:
3
2.5198420997897
-3
4
*/