# Homework Help: Three vectors A, B, and C add together to yield zero

1. Oct 21, 2009

### crono_

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

Three vectors A, B, and C add together to yield zero: A + B + C = 0. The vectors A and C point in opposite directions and their magnitudes are related by the expression: A = 2C. Which one of the following conclusions is correct.

A. B and C have equal magnitudes and point in the same direction.
B. A and B have equal magnitudes and point in opposite directions.
C. B and C have equal magnitudes and point in opposite directions.
D. A and B point in the same direction, but A has twice the magnitude of B.
E. B and C point in the same direction, but C has twice the magnitude of B.

2. Relevant equations

A + B + C = 0

A = 2C

3. The attempt at a solution

I've never been good at these types of problems. They feel like brain teasers. I was thinking about replacing A, B, and C with numbers. A being equal to 2 times C. But that didn't work out as smoothly as I had hoped.

2. Oct 21, 2009

### Gear300

A points in the opposite direction of C, so there is a negative involved: A = -2C.
With this, you can view it as
-2C + B + C = 0 ... (1)
-C + B = B - C = 0 ... (2)
Now you just have to figure out what set of vectors for B satisfy expression (2).

3. Oct 22, 2009

### crono_

Sorry, I'm still not following...

Expression (1) makes sense, but (2) doesn't...