As shown in the figure, there are four points P, a, B and C on the sphere. If PA, Pb and PC are perpendicular to each other, and PA = Pb = PC = a, the surface area of the sphere is______ ．

As shown in the figure, there are four points P, a, B and C on the sphere. If PA, Pb and PC are perpendicular to each other, and PA = Pb = PC = a, the surface area of the sphere is______ ．

If the four points P, a, B and C in space are on the same sphere, PA, Pb and PC are perpendicular, and PA = Pb = PC = a, then PA, Pb and PC can be regarded as three edges from a vertex of a cube, so the sphere passing through the four points P, a, B and C in space is the circumscribed sphere of a cube with edge length a, and the diameter of the sphere is the diagonal of the cube with length 3a, so the sphere area s = 4 π (32a) 2 = 3 π a 2. So the answer is: 3 π A2