If we say r^{2}= (x-a)^{2} + (y-b)^{2} + (z-c)^{2} can generally represent displacement, why can r^{2}= (x- ia)^{2} + (y- ib)^{2} + (z- ic)^{2} generally represent rotation? (i^{2} = -1) And why r^{2}= x^{2 }+ y^{2} + (z - ia)^{2} represents rotation with respect to z axis