The judgment and nature of straight line and straight line, straight line and plane, and plane and plane parallel in the second section of Chapter 9 of the second volume of senior one mathematics (basic module). 1. Let four straight lines A, B, C and D in the space satisfy a//b, b//c, c//d, and try to judge the relationship between A and D. A//D.

Exercise 9.4

1.① Two straight lines perpendicular to the same straight line in space (d)

② Both planes (b) are perpendicular to the third plane.

(3) Plane (b) that passes through two points outside the plane and is perpendicular to the plane.