Am studying stoke's theorem and when doin practice problems have little or no trouble with one exception,

When i have a Surface such as the cone z=(x^2 + y^2)^1/2 with z<= 2

And i parameterize the curve ds c(t) = (2cost , 2sint, 2) it always seems to have the wrong sign, as in answers parameterization is;

c(t) = (2cost, - 2sint, 2).

I'm probably missing something obvious but with all my study brain is fried.

Any help would be greatly appreciated.

Cheers.