This involves solving a 3x3 system of equations, either by substitution or elimination, Cramer's rule, Gaussian elimination, Gauss-Jordan method, or the inverse matrix method, whichever method you have studied.Those three points are on the circle so they will satisfy the equation: Substituting the three vertices gives this system: which simplifies to: Solve that system for D, E, and F and substitute in You solve that. Hint: one of those three values is -3.4, but I won't tell you whether it is D, E, or F. :) Edwin