Display:

$\frac{1+\sqrt{5}}{2}$

Source:

<mfrac>
     <mrow>
          <mn> 1 </mn>
          <mo> + </mo>
          <msqrt>
               <mn> 5 </mn>
          </msqrt>
     </mrow>
     <mn> 2 </mn>
</mfrac>