#11 is incorrect
you should get a line or line segment for #11
for #9, list 4 points such that they all do NOT lie on the same flat surface
#11 would be line LM right? and #9 would be... P,Q,T,N ?
plane LMN is the front face |dw:1440989980794:dw| this face is visible
plane QLS is hidden and it's the left face |dw:1440990010268:dw|
what points do these two planes have in common?
just Q and L, not S
so segment QL is the intersection of those two planes
ie the corner edge where they meet
ah ok got it thanks :)
and is #9 correct?
Q,T,N all lie on the front plane, while P is not on that same plane. So it appears they are noncoplanar BUT notice how they all lie on the "floor" or bottom plane/face |dw:1440990328881:dw|
so they are coplanar.....but there are no other points that fit what the book wants! ;-;
why not move from point P and move upward? |dw:1440990416684:dw| and pick on S instead
or you can change N to M
there are other ways to do it as well
ok makes sense thanks :)