Homework Help: Exam question t/f

1. Sep 13, 2012

Mdhiggenz

1. The problem statement, all variables and given/known data

So I took my calc 3 exam today and had this question

true or false

magnitude ( v+v) = 2*magnitude( v)

I put true.

Thoughts?

2. Relevant equations

3. The attempt at a solution

2. Sep 13, 2012

LCKurtz

You got it correct. Were you just guessing?

3. Sep 13, 2012

Mdhiggenz

No I did a problem where I had to solve for K in the magnitude give the value of v. Pretty much I took k from the magnitude and solved for it. So I was hoping the same thing applied here.

4. Sep 13, 2012

skiller

Really? I don't see how this is correct.

5. Sep 13, 2012

LCKurtz

If $\vec v = \langle a,b,c\rangle$ what do you get for $|\vec v|$ and $|2\vec v|$?

6. Sep 13, 2012

skiller

Sorry, of course it's correct.

I was having a senile moment when I was imagining the two vectors weren't the same! D'oh!

7. Sep 13, 2012

LCKurtz

Don't feel to bad about that. My first reaction was the same because I was expecting the question to read u+v since, in my opinion, that would have been a better question. Only after I started my reply did I realize the OP had v+v.

8. Sep 13, 2012

vela

Staff Emeritus
Did the same thing here.

9. Sep 13, 2012

skiller

I obviously need to learn to read twice before posting. Something which you two are obviously better at than me!

10. Sep 13, 2012

Staff: Mentor

If v happened to be perpendicular to itself, the original statement wouldn't be true.:tongue:

(The zero vector not included, of course.)

11. Sep 13, 2012

skiller

Now you've lost me!

12. Sep 13, 2012

Staff: Mentor

Math humor...

A nonzero vector can't be perpendicular to itself.

13. Sep 13, 2012

LCKurtz

What if it's bent?