It is said that the area of the base of the pyramid and that of the cone are equal. In this case, the are a of the square base is s^2 while the area of circle is pi r^2. Hence, s = sqrt pi * r. The volume of the pyramid has a formula of 1/3 bh. h is equal to 3r. Hence, V = 1/3 bh = 1/3 pi r^2 * 3r = pi r^3.
