# Thread: || u + v || = ?

1. ## || u + v || = ?

Can someone please explain this question to me?

Thanks!

2. Originally Posted by s3a
Can someone please explain this question to me?

Thanks!

u = AB = A(-5,7) to B(3,-5) indicates that vector u = (8,-12)

where u = (8,-12) 8 are horizontal units from A to B
AND -12 are vertical units from A to B

now $\displaystyle ||u+v||= \sqrt{(6+8)^2+ (3-12)^2}$

$\displaystyle = \sqrt{(14)^2+ (-9)^2}$

$\displaystyle = \sqrt{196+ 81}$

$\displaystyle = \sqrt{277}$

3. I'm assuming the AB thing has to with Head - Tail stuff but why is it B - A and not A - B for example?

4. Originally Posted by s3a
I'm assuming the AB thing has to with Head - Tail stuff but why is it B - A and not A - B for example?
The order of these letters matter as they describe dierection.

AB (with the little arrow on top) means from A to B. Where BA means from B to A.

Consider AB = (8,-12) ans BA = -AB

so BA = -(8,-12) =(-8,12)

5. Ok so AB means A is the tail and B is the head and since it's Head - Tail, it's B - A? (just saying it in my own words to see if I understand)