Vectors problem.

**Pupil** · March 2nd 2011, 03:22 PM

ABCD is a parallelogram, where A is (4,2), B is (-6,1) and D is (-3,-4). Find the coordinates of C.

My attempt:
$\vec{AC} = \vec{BD}$
First I'll find the vector $\vec{BD}$ then solve for its magnitude:
$\bec{BD} = \vec{OD} - \vec{OB} => (-3-(-6),(-4-1) => (3,-5)$
Now I'll find the magnitude:
$\vec{BD} = \sqrt{(3)^{2}+(-5)^{2}}$
$\vec {BD} = \sqrt{34}$
Unfortunately, this is the farthest I can get. I tried isolating for $\vec{C}$ but didn't work out as I only got 1 value and not two. I don't have the slightest clue on how to solve this problem (never saw it in my work or problems) and it threw me off completely. Thanks in advance.