If you attempt to use Formula 2 to find the area of the top half of the sphere x² + y² + z² = a², you have a slight problem because the double integral is improper. In fact, the integrand has an infinite discontinuity at every point of the boundary circle x² + y² = a². However, the integral can be computed as the limit of the integral over the disk x² + y² < t² as t→ a^-. Use this method to show that the area of a sphere of radius a is 4πa².