A Beginner's Guide to MathML
Roots
For displaying a square-root MathML provides the <msqrt> tag:
<msqrt>
<mi>x</mi><mo>+</mo><mn>2</mn>
</msqrt>
For more general roots there is the <mroot> tag. Unlike the <msqrt>, which can contain any number of child tags, the <mroot> must contain exactly two. Again the order is important: the first element is the expression being rooted, and the second is the power of the root.
Below is an example of a cubic root in which, to satisfy the two child rule , the expression being acted upon is grouped within an <mrow> tag:
<mroot>
<mrow>
<mi>x</mi><mo>+</mo><mn>2</mn>
</mrow>
<mn>3</mn>
</mroot>