<math xmlns="http://www.w3.org/1998/Math/MathML">
  <apply><in/>
    <ci>x</ci>
    <set>

      <apply><divide/>
        <apply><plus/> <!-- upper root -->
          <apply><minus/>
            <ci>b</ci>
          </apply>
          <apply><root/>
            <apply><minus/>
              <apply><power/>
                <ci>b</ci>
                <cn>2</cn>
              </apply>
              <apply><times/>
                <cn>4</cn>
                <ci>a</ci>
                <ci>c</ci>
              </apply>
            </apply>
          </apply>
        </apply>
        <apply><times/>
          <cn>2</cn>
          <ci>a</ci>
        </apply>
      </apply>

      <apply><divide/>
        <apply><minus/> <!-- lower root -->
          <apply><minus/>
            <ci>b</ci>
          </apply>
          <apply><root/>
            <apply><minus/>
              <apply><power/>
                <ci>b</ci>
                <cn>2</cn>
              </apply>
              <apply><times/>
                <cn>4</cn>
                <ci>a</ci>
                <ci>c</ci>
              </apply>
            </apply>
          </apply>
        </apply>
        <apply><times/>
          <cn>2</cn>
          <ci>a</ci>
        </apply>
      </apply>

    </set>
  </apply>
</math>