It would be easier to help you if you could provide the text of that biomechanics expression including that Greek symbol!
Apologies - that was an obvious omission:
F ∝ ρ.A.v2
a = Dv / Dt (actually the D here should have been the Greek letter delta)
F= μ x N
I cannot reproduce the problem - either on 1.9 or 2.0. The examples you give display OK.
Do those expressions appear in the glossary concept field or definition (the latter, I presume).
Moodle 1.9 or 2.0?
Greek characters not displayed when viewing the glossary itself or in the glossary popup window which appears when clicking on the glossary autolinks in a text on your site?
Please provide as many details as possible, including screenshots, export your "problem glossary" (or part of it) and attach it to a further post here so I can examine it.