The <mroot> MathML element is used to display roots with an explicit index. Two arguments are accepted, which leads to the syntax: <mroot> base index </mroot>.
This element accepts the global MathML attributes.
<math display="block">
<mroot>
<mi>x</mi>
<mn>3</mn>
</mroot>
</math><msqrt> (Square root without an index)