Just a quick question

how do you type in,

tan-1(-5/2) (or any negative number)

on the calculator?? or just work it out?

CompuChip
Are you talking about the (-5/2)? Most calculators have a separate key for that, which usually has something like "(-)" printed on it (a short dash in parentheses), rather than the normal (longer) minus sign "${}-{}$".