Because the rectangular system vectorized to the left of the plane has become a spatial concept, the coordinate representation of the vector can also be understood as a straight line, such as OA( 1, 4), which is actually a straight line connecting the point (1, 4) and the coordinate origin, and its slope is 4. No matter what the abscissa takes, the slope will not change. The linear equation of these two points is y=4x. Now it is known that the projection of these two vectors on the direction vector of another straight line is the same, so this straight line is limited in terms of condition and slope, so for the convenience of product operation, it is set to 1, that is, the slope mentioned above has nothing to do with coordinates.