<?php
function f($x) {return (-$x*$x+6*$x-3);}

function find($l,$r,$eps,$f)
{ while (($r-$l)>$eps)
  { $m1 = $l + ($r-$l)/3; 
    $m2 = $r - ($r-$l)/3;
    if ($f($m1) < $f($m2)) $l = $m1; else
    if ($f($m1) > $f($m2)) $r = $m2;
    else {$l = $m1; $r = $m2;}
  }
 return [($l+$r)/2, $f(($l+$r)/2)];
}
[$x, $y]= find(-10,10,0.000000001,'f');
echo "Максимум функції f(".$x.") = ".$y;
?>