Let D: x ^ 2 + y ^ 2 + Z ^ 2 = a ^ 2, then what is the area of ∫ (x + y + Z) ^ 2ds curve divided into? (on D) The answer is 4 Π a ^ 4

Let D: x ^ 2 + y ^ 2 + Z ^ 2 = a ^ 2, then what is the area of ∫ (x + y + Z) ^ 2ds curve divided into? (on D) The answer is 4 Π a ^ 4

It is considered that the surface is a sphere. According to the involution of the surface, the integral of the first term containing x, y and Z is equal to 0
Original integral = ∫ (x + y + Z) ^ 2 DS = ∫ (x ^ 2 + y ^ 2 + Z ^ 2 + 2yz + 2zx + 2XY) ds = ∫ (x ^ 2 + y ^ 2 + Z ^ 2) ds
=a^2 ∫dS
=A ^ 2 * (area of integral surface)
=a^2*4πa^2
=4πa^4