- A
- B
- C
- D
View written solutionFree
Correct answer: NONE OF A, B, C, D
We need the lines which can be an edge of some tetrahedron whose two faces lie on and .
1. Key geometric idea
If two faces of a tetrahedron lie on planes and , then these two faces intersect along an edge of the tetrahedron.
So the required line must be the line of intersection of the two planes and .
Thus, among the given options, we must find which lines coincide with
2. Find the intersection line of and
The planes are:
So,
Multiply (2) by :
Add to (1):
Substitute in (2):
Hence the intersection line is given by
Let . Then
A convenient parametric form is obtained by taking :
So the line is
Any equivalent direction vector is acceptable, e.g. .
3. Check each option
Option A
This means So direction vector is .
This line is parallel to the -axis and does not satisfy or for all points. Hence it is not the intersection line.
So A is incorrect.
Option B
So
Check if every point lies on both planes.
For : This is not identically zero.
Hence line is not in ; so it cannot be the common edge. Thus B is incorrect.
Option C
So
For : not identically zero.
So C is incorrect.
Option D
So
For : not identically zero.
So D is incorrect.
4. Conclusion
None of the given lines equals the line of intersection of and .
Therefore, none of the options can be the edge common to the two faces lying on and .
So my derived answer is:
5. Comparison with stored answer
Stored correct answer: A, B, D
This does not match the geometric requirement. The common edge of the two faces must lie on both planes simultaneously, i.e. it must be their line of intersection. None of A, B, C, D satisfy both plane equations identically.
Hence I disagree with the stored answer.
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