# A simple question about coordinate sytems

## Main Question or Discussion Point

Hi I didn't post this in homework help, as I didn't feel my question belonged there. If it doesn't belong here, my apologies.

I recently took an exam and it turns out I got the first question wrong according to my professor. The problem states:
"In the diagram four vectors are represented by arrows in the xy plane. Each division represents 1 meter" "What is vector d?"
Because the problem stated it was in the XY plane I put the answer as <-3,4>, but my professor took off a point for not accounting for the z coordinate.

I'd like a second opinion please.

http://gyazo.com/b54c3535fd7fd5f95138e7af3e68d786.png [Broken]

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## Answers and Replies

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Drakkith
Staff Emeritus
Science Advisor
Did your homework questions on this subject usually have you write the Z coordinate even when zero or when the problem was stated to be in an XY plane?

Yes, but on our homework questions it would clearly state it was an XYZ coordinate system and include a Z axis. I thought the problem was a trick question to make sure we were paying attention and not writing the z just for the sake of writing it.

Here is a similar homework problem:
http://gyazo.com/4b63e64b66621fa1a50f41cec00146e7.png [Broken]

I think that problem alone warrants me to the right to question my professors solution.

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Drakkith
Staff Emeritus
Science Advisor
I'd talk to your instructor, explain what went on in your mind, and then see if he will give the point back. If he won't, then I'd ask him to change the question to state it was an XYZ plane in order to avoid future confusion. In any case I'd say it's up to him. Of course, if you REALLY want to get into it you can always go to whoever is above him.

Drakkith
Staff Emeritus
Science Advisor
I think that problem alone warrants me to the right to question my professors solution.
Personally I agree. Just remember that if you're ever confused on what a question is asking you, ask the instructor or test proctor or whoever.

Thank you very much Drakkith. I hate confrontations, but I'll go to her office hours soon. This is resolved.