<?php
    $max = 10; 
    $var2 = 0;
 
    for($i = 0; $i <= $max; $i++){
      $var3 = $var2; // Neste momento o $var2 ainda não pegou a linha atual
                     // consequentemente, terá sempre o valor da linha anterior
                     // ou zero, na primeira iteração (já que definimos zero fora do loop)
      $var1 = $i * 100;
      $var2 = $var1 * 50;
 
      // Agora já temos $var1, $var2 e $var3 definidos, sendo que 1 e 2 são
      // da linha corrente, e o 3 da anterior
      echo '$var1:' . $var1 . ' - $var2:' . $var2 . ' - $var3:' . $var3 .PHP_EOL;
    }

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