Question

How does A compare to B a=cos(0+2pi) b=cos(-0)

Answer 1

You can use the double angle formula for A.
Cos(0 + 2pi) = Cos(0)*Cos(2*pi) - Sin(0)*Cos(2*pi)
Cos 0 = 1
Cos (2*pi) = 1
Sin(0) = 0
So you are left with cos(0 + 2pi) = 1 * 1 = 1

there are a couple of ways of handling Cos(-0) 
The First and most obvious way is to put it in your calculator just as you see it. Most calculators would do it like this
Cos(
+/-
0
)
=
The result should be 1
You could try using cos(0-0) You will get the same answer -- 1.