Suppose that the graph of 2x^2 + y^2 + 8x - 10y + c = 0 consists of a single point. (In this case, we call the graph a degenerate ellipse.) Find c.
Completing the square, I get (x + 4)^2 + (y - 5)^2 + c - 41 = 0, so c = 41.