Given point P(x,y,z)

From the figure, we can say that Point E (x,y,0) is the projection of Point P on the XY-plane ( the z-coordinate remains zero on XY-plane).

Distance between two points is given by

Here the distance between Point P & E will give the distance of the point P from the XY-plane.

Here a₁ = x, b₁ =y , c₁ =z

a₂ = x, b₂ = y, c₂ = 0

Distance from P to E =

= √ (-z)²

= √ (z)²

= z

Therefore, the distance between the XY plane and point P is z units.