the problem here is this vector must be found from c = A\b. A and b are created from two variables x and y. (I posted the image of example xi,yi). x and y come from the normal parabola(ax^2 + bx +c) first, then they could be used in the matrix to form A and b. if my question is too confusing, just see the image...sorry, I am not good at explaining a problem :c Is there a way to solve it ? Thank you.