Vector Addition and Subtraction in Three Dimensions

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Homework Statement

Point A (2i +j 2k)
Point B (3i +2j +5k)
Point C (4i +5j -2k)

the point d is such that abcd in that order is a parallelogram.

Find position Vector D

Homework Equations

The Attempt at a Solution

ok so i start of like this but I am getting the wrong answer.
http://img511.imageshack.us/img511/5946/vectorak5.jpg

(BA)^1/2=(CD)^1/2

but its wrong.

 

[NateTG]

It might be useful to make a drawing.

 

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Yes, but are those equations correct
I've realized my error.
culd you tell me the point of the unit vector.

 

[NateTG]

You don't need to do anything involving norms or unit vectors here, so the square root stuff is way off base. It's really just a matter of vector addition, and subtraction.

$$\vec{BA}=\vec{OD} - \vec {OC}$$
makes sense to me, the other equations don't really.