# vector question - parallelogram

• May 4th 2010, 06:48 AM
shawli
vector question - parallelogram
The question and the solution are attached in this post.

I don't understand the solution to question a) ii., could someone please explain it to me?
• May 4th 2010, 09:34 AM
tonio
Quote:

Originally Posted by shawli
The question and the solution are attached in this post.

I don't understand the solution to question a) ii., could someone please explain it to me?

It's just cumbersome notation: note that since ABCD is a paralellogram, it must be that $AD=BC\,,\, \|AD\|=\|BC\|\,,\,AD//BC\Longrightarrow \overrightarrow{AD}=\overrightarrow {BC}$ , and

putting $D=xi+yj$ , we get that $\overrightarrow{AD}=(x-4)i+(y-2)j=-6i-2j=\overrightarrow{BD}\Longrightarrow x=-2\,,\,y=0\Longrightarrow D=-2i$

Tonio
• May 4th 2010, 09:44 AM
shawli
Ohhh I see it ...drawing it helps.

Thank you!!