# Homework Help: Vectors are parallel

1. Sep 7, 2011

### tarheels88

1. The problem statement, all variables and given/known data
Given vectors b and c are they parallel? If so find such scalar s that c=sb, otherwise write N for no.

a) b=<0,3,4>, c=<0,6,-8)

b) b=<10,6>, c=<-15,-9>

2. Relevant equations

c=sb is a property of the dot product.

3. The attempt at a solution
For a) I put No because <0,6,-8> does not = <0s, 3s, 4s> because S=2
For b) I put Yes because S=-3/2 which would give you both outcomes of the vectors

Am I correct?

2. Sep 7, 2011

### Dick

Yes, you are. If you'd explain why you need to pick s=2 in the first case, that would probably help. "because s=2" isn't much of an explanation.

3. Sep 7, 2011

### tarheels88

I put s=2 because I was finding a multiple of the two vectors given. Then I calculate 3s=6, that would then calculate to c=2.

4. Sep 7, 2011

### Dick

Right, so the only possibility is s=2, and since that doesn't work there is no s that works. I knew you knew that. Just wanted you to add that if you are turning this in as a homework exercise.