pecial">&lt;&lt;</span> <span class="identifier">x2</span><span class="special">);</span>

  <span class="comment">// from Vieta formula</span>
  <span class="keyword">double</span> <span class="identifier">minus_b</span> <span class="special">=</span> <span class="identifier">x2</span> <span class="special">+</span> <span class="identifier">x1</span> <span class="special">-</span> <span class="special">(</span><span class="identifier">fx2</span> <span class="special">-</span> <span class="identifier">fx1</