A plane is determined by three non-collinear points, by a line and a point outside it, by two intersecting lines, or by two parallel lines.
Two lines in space are parallel, intersecting, or skew.
A line perpendicular to two intersecting lines in a plane is perpendicular to the whole plane.
The distance from a point to a plane is the length of the perpendicular from the point to the plane.
The space diagonal of a cube of edge a equals a√3. In the cube of edge 4 cm, the diagonal makes an angle θ with the base where sin θ = 1 ÷ √3 (the same for every cube).