Let the screen be a plane.[br][br]Move points [i]A[/i] and [i]R[/i] to represent any vector on the plane.[br][br]Change the direction of vectors [b]m1[/b] and [b]m2[/b].[br]Make sure they are non-parallel.[br][br]Then vector AR can be represented as a linear combination of [b]m1[/b] and [b]m2[/b].