1: P is a point on the first straight line. If z=λ, then Y = λ and X = 1, then the coordinate of p can be written as (1, t, t).
2. According to the meaning of the question, PQ and the second straight line are in the same plane, and P and the second straight line are naturally in the same plane. According to the equation of point and straight line, we can get the equation (a) of the plane where P and the second straight line lie.
3. Similarly, we can get the equation (b) of the plane where P and the third straight line lie.
4. According to the equations of planes A and B, we can get the linear equation of PQ.
5. You can get the trajectory equation of a straight line by eliminating λ in the equations (this step needs a little understanding).