If x,y,zx, y, zx,y,z are in arithmetic progression, then x2+2yz+z2x^2 + 2yz + z^2x2+2yz+z2 is equal to:
(x+z)2(x+z)^2(x+z)2
4y24y^24y2
x2+z2x^2+z^2x2+z2
2(x2+z2)2(x^2+z^2)2(x2+z2)