# Thread: Vector length problem

1. ## Vector length problem

Hello, how do I solve the following problem?

2. ## Re: Vector length problem

Originally Posted by Artifact
Hello, how do I solve the following problem?
Do you know how to find $\displaystyle 2\vec{a}-3\vec{b}~?$

If you do know how to do that, the just do it then find the length of the result.

If you do not, please explain why not. Because you are being asked to do somethings that you don't understand.

3. ## Re: Vector length problem

so I guess 2a is 2* 29 and 3b is 3*58? Or am I off track?

4. ## Re: Vector length problem

Originally Posted by Artifact
so I guess 2a is 2* 29 and 3b is 3*58? Or am I off track?
Originally Posted by Plato
Do you know how to find $\displaystyle 2\vec{a}-3\vec{b}~?$
If you do know how to do that, the just do it then find the length of the result.

If you do not, please explain why not. Because you are being asked to do somethings that you don't understand.
You did not answer any of those questions!

WHAT IS $\displaystyle 2\vec{a}-3\vec{b}=~?$

5. ## Re: Vector length problem

ok, I guess I don't know how to find 2a-3b, I thought I had to find the length of a first and then find the length of b. After that I would multiply a with 2 and b with 3. So 2a-3b would be = 58 - 174. But I guess that is the wrong way of doing it.

6. ## Re: Vector length problem

Originally Posted by Artifact
ok, I guess I don't know how to find 2a-3b
Why are you asked to do something you clearly are not prepared to attempt?
That makes no sense.

7. ## Re: Vector length problem

Originally Posted by Artifact
ok, I guess I don't know how to find 2a-3b, I thought I had to find the length of a first and then find the length of b. After that I would multiply a with 2 and b with 3. So 2a-3b would be = 58 - 174. But I guess that is the wrong way of doing it.
Hi there (=. Before we start let us understand how scalar multiplication and subtraction of vectors works.

Scalar multiplication:

Subtraction of two vectors
can be geometrically defined as follows: to subtract b from a, place the end points of a and b at the same point, and then draw an arrow from the tip of b to the tip of a. That arrow represents the vector a − b, as illustrated below:

The difference of a and b is

now find the resulting vector and find it's magnitude which you seem to know how to do.

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