Help with Vectors in R^3 - Noob Question

[sibiryk]

First I want to say hello to everyone in here. I'm a noob.

Here is my problem.
Let u=(1.2.0), v=(0,0,3), and w=(0,1,0) are vectors in R^3.
Evaluate, if defined, the following expretions (if undefined state so)

a) (u * v)w
b) u+w*v
c) (u * u)/w
d) (v * v)/(w * w)


Should I try to calculate them or just tell if expretion is defined or undefined?
How can I tell if expretions above are defined?

 

[James R]

Should I try to calculate them or just tell if expretion is defined or undefined?

Read the instructions in the question!

Is "*" supposed to represent a dot product, or cross product?

 

[sibiryk]

Read the instructions in the question!

Is "*" supposed to represent a dot product, or cross product?

It is a dot product.

 

[EnumaElish]

"Evaluate" means "calculate."

If you calculate and get a definite answer (a real number or vector) then it is defined.

 

[sibiryk]

Are my answers correct?

a) 0
b) undefined ( I don't see how I can add scalar to vector)
c) undefined
d) 9

 

[HallsofIvy]

a, b, c are correct (you are correct that you can't add a scalar to a vector. In c, division by a vector is not defined). However, in
d) (v * v)/(w * w)
The answer is clearly a fraction.

 

[James R]

The answer to (d) is correct. It's 9.

 

[HallsofIvy]

Hey, 9/1 is a fraction! (blushing)