joe m 🐀

I want to write this

<math>
<mfrac>
  <mrow>
    <mo>−</mo><mi>b</mi><mo>±</mo>
    <msqrt>
      <msup>
        <mi>b</mi><mn>2</mn>
      </msup>
      <mo>−</mo><mn>4</mn><mi>a</mi><mi>c</mi>
    </msqrt>
  </mrow>
  <mrow>
    <mn>2</mn><mi>a</mi>
  </mrow>
</mfrac>
</math>

but I cannot

−b± b2 −4ac 2a

code and (nonfunctional) render below the cut