# Naming Coplanar Points?

Question is:   Name a point that is coplanar with points B, C, and G.

I don't think B and G are coplanar because they are in different planes.  It doesn't make sense to find fourth point that is coplanar with three given points.  It looks like three given points themselves are not coplanar.

This is high school geometry  problem.

The figure needed to solve this problem is attached.
LVL 1
###### Who is Participating?

Commented:
Every set of 3 points is coplanar.
This particular plane will cut the box in half along the CG face diagonal.
It will also go through point H by symmetry.
0

Author Commented:
Sorry,  forgot to attache the figure.
coplanar-figure.jpg
0

Commented:
Imagine the plane that contains ABCD, the top of the box.
You can rotate this plane around the BC axis until it hits G.  This is the plane you want.
It will contain the BC segment by definition, and the GH segment by symmetry.
0

Commented:
Can we assume the figure is symmetric?  If so, then I agree H should be coplanar with the other 3.

If the EH edge is shorter or longer than FG then no named point will be coplanar with BCG
0

Commented:
d-glitch has given you the essential information. As he said ANY three points can be used to define a plane. A possible solution for your problem is to find the equation for your plane.
If you want your can rotate your coordinate system to set the plane in the xy plane. Then any two mumbers would represent a point on your plane.
0

Author Commented:
>>  This particular plane will cut the box in half along the CG face diagonal.

This half box is not a plane until it is physically straightened so it becomes flat.  Am I correct?

>> Imagine the plane that contains ABCD, the top of the box. You can rotate this plane around the BC axis until it hits G.

So, this will give same result as your other example.  Correct?
0

Commented:
sdstuber, given that it's a high school geometry question, I'm sure we can assume that it's just a rectangular prism so d-glitch's answer is correct.
0

Commented:
I agree it's probably correct, but some of the rules of geometry drilled into me in high-school was that just because the drawing "looks" symmetric doesn't mean it is.  Just because an angle "looks" like a right angle doesn't mean it is.

The question and answer could be just as valid and high-school level to say "unknown" because answering "H" means relying on the "look" to declare symmetry.
0

Author Commented:
Are there other correct answers besides point H?

What if we take the right side (plane DCGF) and lift it up 90 degrees, now we have plane
ABCDGF.

Now, points A, D, and F are coplanar with points B, C, and G.  Am I correct or incorrect?
0

Commented:
No. You can't actually move things. d-glitch was just trying to give you a visual.

Try it this way:
Draw lines CH and BG. See how they form an X in the "diagonal plane" of the box?
The fact that something is coplanar doesn't mean the plane has been drawn, just that it could be drawn (i.e. it exists).

So the plane that connects those four points isn't currently drawn in the figure, but you could draw it. Thus, they are coplanar. Don't move any points.
0

Commented:
Another way of looking at it. If you had the real 3D figure and took a sheet of paper and aligned with B, C, and G. Notice that it will also touch H. The paper represents the plane.
0

Author Commented:
Multiples solutions,  Multiple explanations.  Follow up great explanations.  Tremendous help.
They really explained from all angles.  It's impossible not to understand!

Thank you so much!
0
Question has a verified solution.

Are you are experiencing a similar issue? Get a personalized answer when you ask a related question.

Have a better answer? Share it in a comment.