# Math Help - Vectors: i + i = ?

1. ## Vectors: i + i = ?

Good day folks,

I realise i x j = k, i x i = 0 etc.

Can someone tell me if there are relations for i + i and i/i ?

I apologise - I am a bit rusty with this stuff...

Kind regards.

2. ## Re: Cartesian co-ordinates i + i = ?

Originally Posted by paulbk108
Good day folks,

I realise i x j = k, i x i = 0 etc.

Can someone tell me if there are relations for i + i and i/i ?

I apologise - I am a bit rusty with this stuff...

Kind regards.
i + i = 2i.

Dividing vectors is not defined so i/i is not defined.

There are many websites that explain the algebra of vectors in detail, I suggest you use Google to find one.

3. ## Re: Cartesian co-ordinates i + i = ?

Very good. Thank you. Simple.

What about i + j = ? Or is that not defined as well?

Regards.

4. ## Re: Cartesian co-ordinates i + i = ?

I have an example here that goes from

1.2i + 1.2j + 0.7i + 0.7j
= 1.2 + 0.7

I just can't figure out why...

Regards.

5. ## Re: Cartesian co-ordinates i + i = ?

Originally Posted by paulbk108
I have an example here that goes from
1.2i + 1.2j + 0.7i + 0.7j= 1.2 + 0.7
That is completely wrong.
If it is as you posted it then
$1.2i + 1.2j + 0.7i + 0.7j=1.9i+1.9j$.

So please check the exact wording of this problem!

6. ## Re: Cartesian co-ordinates i + i = ?

I have

-(Vc)i = -1.2i + 1.2j + 0.7(Vc)i + 0.7(Vc)j

=> -(Vc) = -1.2 + 0.7(Vc)

Not sure if that makes a difference.

7. ## Re: Cartesian co-ordinates i + i = ?

Originally Posted by paulbk108
I have

-(Vc)i = -1.2i + 1.2j + 0.7(Vc)i + 0.7(Vc)j

=> -(Vc) = -1.2 + 0.7(Vc)

Not sure if that makes a difference.
This statement comes from the dark side of the moon. Clear things up ... what is the original problem and what is it asking you to determine?

8. ## Re: Cartesian co-ordinates i + i = ?

Solving for Vca.

-Vci = (3k) x (0.4i + 0.4j) + ((Vca)cos45i + (Vca)sin45j)
=> -Vci = -1.2i + 1.2j +0.7(Vca)i + 0.7(Vca)j
=> -Vc = -1.2 + 0.7(Vca)
=> 0 = 1.2 + 0.7(Vca)
=> Vca = -1.697 m/s

=> Vc = 2.4 m/s.

I hope that clears it up. I also hope you can assist me further...

Regards.

9. ## Re: Cartesian co-ordinates i + i = ?

Originally Posted by paulbk108
Solving for Vca.

-Vci = (3k) x (0.4i + 0.4j) + [(Vca)cos45i + (Vca)sin45j]
to tell you the honest truth, this makes absolutely no mathematical sense to me.

is that a cross product at the start?. what does "k" represent?

why don't you "copy" the original problem, upload it to imageshack, and post it as a link so that someone can make sense of it?

10. ## Re: Cartesian co-ordinates i + i = ?

Attached is the solution in question. Hope now it is a bit clearer.

Regards.

11. ## Re: Cartesian co-ordinates i + i = ?

Originally Posted by paulbk108
I have

-(Vc)i = -1.2i + 1.2j + 0.7(Vc)i + 0.7(Vc)j

=> -(Vc) = -1.2 + 0.7(Vc)

Not sure if that makes a difference.
Writing your equation in LaTeX gives:

$-(V_c)\hat{i} = -1.2\hat{i} + 1.2\hat{j} + 0.7(V_c)\hat{i} + 0.7(V_c)\hat{j}$

Equating the x components, then solving for V_c gives your result.

Equating the y components gives the same result.