span><span class="special">)</span> <span class="special">/</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="keyword">double</span> <span class="identifier">c</span> <span class="special">=</span> <span class="special">(</span><span class="identifier">x1</span> <span class="special">*</span> <span class="identifier">fx2</span> <span class="special">-</span> <span class="iden