Mathematics is, as Jim Reynolds said, singular despite being plural in form. There are various other words like it, including many other words ending in -ics such as physics,dynamics, ethics, linguistics, metaphysics, optics, economics.
I think Physics is Singular only if you talking about just one system of physics. So if your talking about more systems of physics then it will be Plural.Mathematics is singular, although it seems to be Plural its most commonly used with a verb in singular form. Hope this helps!
