In Figure, if the coordinates of P are (a, b, c), then the reflections or images of P in XY, YZ and ZX-planes are

(a, b, -c), (-a, b, c), (a, -b,c)

The reflection or image of P (a, b, c) in xy-plane will be as much below the xy-plane as point P is above it, that is, if P' is the reflection of P in xy-plane, then P' D = PD = c and P' D is parallel to OZ'. So, the coordinates of P' are (a, b, -c).

The image of P (a, b, c) in yz-plane will be as much on the back side of yz-plane as the point P is on its front side. Thus, if P" is the image of P in yz-plane, then P" lies on PE such that PE=EP".

But, PE=OA = a. So, the coordinates of P" are (- a, b, c).

The image of P (a, b, c) in zx-plane will be as much as on the left side of xz-plane as the point P is on its right side. Thus, if P''' is the image of P in zx-plane, then P''' lies on PF produced such that PF = FP'"'. But, PF = OB = b. So, the coordinates of P''' are (a, -b, c).