If given a list of 4 input/output values in a table, which set of input/out values do I start with to find a rule?

Me, prove a quadrilateral with vertices g(1,-1), h(5,1), i(4,3) and j(0,1) is a rectangle using the parallelogram method and a rectangle method.

Find the center and the radius of the circle with the equation: x^2-2x+y^2+4y+1=0?

I'm confused on this could anyone me and show me what i need to do to solve it.