Find an expression for the function whose graph is the given curve.

Question

a) The bottom half of the parabola x+(y-1)^2=0
b) The top half of the circle (x-1)^2 + y^2= 0

I think I have a vague idea of what I need to have in my expression for b; I know it's a circle with a center (1,0) and a radius of 1, so the range is [0,2] and the range [that we're concerned with] is [0, 1]. I think I might need to use the absolute value of x in there somewhere, but other than that I don't know what to do. For both a) and b), I don't really know how to formulate an expression for a function where the slope is not constant. Any help would be appreciated.