Often the solution of any difficult task of descriptive geometry comes down to the solution of a set of small tasks, including tasks of finding of a straight line parallel to the set plane.
Instruction
1. Designate the plane by three points and find all their projections on the set types. You have to remember that projections of points lie on the same lines of projective communication. If in your case the plane is set by a straight line and a point, you can choose missing two points on a straight line randomly, proceeding from own preferences. If your plane is set by the crossed straight lines, you can choose all three points randomly, however in this case it is better for one of points to use a point of intersection of the mentioned straight lines. Connect the received three points straight lines on both planes of projections.
2. Draw a straight line in the plane so that its beginning coincided with any point of the plane, and the end concerned any party. Designate both points and find missing projections by means of lines of projective communication. Designate the turned-out straight line. This straight line belongs to the plane because definition extends to it: "The straight line belongs to the plane in only case when it passes through two points belonging to this plane".
3. In any place on any of the planes of a projection draw the straight line parallel to a projection of that straight line which you drew in the previous step (the straight line belonging to the plane) and designate it. Construct a missing projection of a new straight line (it will be also parallel to a projection of the straight line belonging to the plane). The new straight line will also be direct, parallel this plane.