1. The problem statement, all variables and given/known data For what values of a do the points (4,3),(-3,1),(1,a), and (1,5) lie on a circle? 3. The attempt at a solution So my solution came down to getting the equation a(x^2+y^2)+bx+cy+d=0 Making a matrix with the first three points, doing R1-R4, R2-R4, R3-R4, then reducing the matrix to a 3X3. After that you have the equation then sub in the last point and you get something like 0=-32a^2 - 344. My problem is that I am getting a square root of a negative number, what did I do wrong?