The first one is just a plane that intersects z at -2. Think about it, whatever x and y are, the point lies at z = -2, so it is a plane:

The 2nd and third one must be dealt with using the following:

z = g(x,y) = cos(y)

So that:

a = cos(y)

and

z = h(x,y) = 1-x

So:

a = 1 - x