Line of intersection of two planes

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SUMMARY

The discussion clarifies that the line of intersection of two planes can be determined using the cross product of their normal vectors. The normal vector of a plane is defined as perpendicular to any line within that plane. Consequently, the cross product results in a vector that is perpendicular to both normal vectors, establishing its parallelism to the line of intersection, which exists within both planes. It is important to note that the cross product yields a direction vector, not a specific line in space.

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Hi,
I am having difficutly figuring out why the cross product of the normal vectors of each plane gives the direction vector of the line of intersection. Anyone care to try to explain?


Thanks!
 
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The line of intersection lies in both planes. The normal to a plane is (by definition) perpendicular to any line in the plane. The cross product then gives you a line perpendicular to both normals, so that it must be parallel to the line of intersection.
 
mathman said:
The line of intersection lies in both planes. The normal to a plane is (by definition) perpendicular to any line in the plane. The cross product then gives you a line perpendicular to both normals,
therefore lieing in both planes, therefore along the line of intersection
so that it must be parallel to the line of intersection.
 
therefore lieing in both planes, therefore along the line of intersection

The cross product is a vector, NOT a line is space - that is, it has a direction but no position. Therefore it doesn't lie anywhere, but it is parallel to the line of intersection.
 

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