Question

What could be the intersection of plane PRS and plane QRS?

A.
RS
←
→

B.
PR
←
→

C.
QS
←
→

D.
The planes need not intersect.

Answer 1

The plane PRS passes through the points P, R and S. So it contains the line RS. Also the plane QRS passes through the points Q, R and S. So it contains the line RS as well. Since both the planes contain the line RS, the line RS must be the intersection of plane PRS and QRS. So the answer choice is A.