Consider the following curve: (x² + y²)² = x² + 4 You can assume throughout this problem that this curve is differentiable at every point other than (0,0). Ignore the point (0,0) for this question. Prove that there are exactly 6 points on the curve with horizontal tangent lines. Find the coordinates of these points. (Hint: Think of y as a function of x, and use implicit differentiation. You should find that 4 of the points lie on a common circle of the form x² + y² = r²).