16(c)I.
Solving simultaneously: x^2 +(y-c)^2=r^2 and y=x^2 for the coordinates of the touching points,
Hence : y+(y-c)^2=r^2, which is a quadratic equation in y.
Buy the touching points are equal in y coordinates, so discriminant of the equation equals to 0.
So (1-2c)^2 - 4 (c^2 - r^2 = 0...