# How do I write ultimate equality in mathjax?

The above symbol is referred to as ultimate equality in Tristan Needham's Visual Differential Geometry. How do I write it in latex?

You can use \asymp to get $$\asymp$$ (for "is asymptotic to").
A good resource is DeTeXify; you can draw the symbol you want and it will provide possible $$\LaTeX$$ codes for it. Note, however, that MathJax does not support all packages, so some of the options may not be available.
For this picture, it suggests \asymp, $$\asymp$$ as noted by Peter Phipps, which is regular $$\LaTeX$$ and so supported.