Display:

$\frac{1}{x^3+\frac{x}{3}}=\raisebox{1ex}{$1$}\!\left/ \!\raisebox{-1ex}{$x^3+\frac{x}{3}$}\right.$

Source:

<mfrac>
     <mn> 1 </mn>
     <mrow>
          <msup>
               <mi> x </mi>
               <mn> 3 </mn>
          </msup>
          <mo> + </mo>
          <mfrac>
               <mi> x </mi>
               <mn> 3 </mn>
          </mfrac>
     </mrow>
</mfrac>
<mo> = </mo>
<mfrac bevelled="true">
     <mn> 1 </mn>
     <mrow>
          <msup>
               <mi> x </mi>
               <mn> 3 </mn>
          </msup>
          <mo> + </mo>
          <mfrac>
               <mi> x </mi>
               <mn> 3 </mn>
          </mfrac>
     </mrow>
</mfrac>