Find a comment line which have only one $ symbol using regex?

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regular-expression

I have file with more comment lines.
Some comment lines have single $ symbol.
How to find that line?


Ex,
1. %\documentclass{acm_proc_article-sp}
2. %\fntext[labelHS]{PhD}
3. %Multi-DBSCAN chooses the best $\epsilon$ for each density distribution using an outlier detection algorithm
4. % and its value is constrained as: $\alpha>1$
5. % \REQUIRE List of mcd$:list of mini core distance
6. % \REQUIRE List of $cmc$: core mini cluster
7. % and its value is constrained as: $\alpha>1


i want a regex that choose a comment line with Single $ only.
That Regex Select 5 and 7 line.

Could anyone help me?