# Three vectors lie in an xy plane

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1. Sep 5, 2015

### 0btuse

1. The problem statement, all variables and given/known data
Three vectors A, B, C, each have a magnitude of 46 m and lie in an xy plane. Their directions relative to the positive direction of the x axis are 28 ˚, 191 ˚, and 313 ˚.

What are the magnitude and the angle of A-B+C with right-arrow in the range of (-180°, 180°)?

2. Relevant equations

3. The attempt at a solution
Nx = 46cos(28)-46cos(191)+46cos(313)= 117.15
Ny = 46sin(28)-46sin(191)+46sin(313) = -3.26

N= sqrt((117.15^2)+(-3.26)^2)
N = 117.11

For the angle i have tan^-1 (-3.26/117.15) = -1.60°

the online homework is accepting my answer for the angle as being correct, however i'm not as fortunate with the magnitude.

2. Sep 5, 2015

### TSny

Your method is correct. I get a slightly different answer when I calculate the magnitude. It differs in the fourth digit. I don't know how accurate your answer needs to be.

3. Sep 5, 2015

### 0btuse

i suppose i'll have to take the hit on the assignment because no matter how I round it's not accepting my answer. I've tried adding additional sigfigs to no avail. thank you for your response. it's been driving me crazy.

4. Sep 5, 2015

### TSny

Edit: It looks like when you calculated the magnitude you might have calculated it as $\sqrt{117.15^2 - (3.26)^2}$ rather than $\sqrt{117.15^2 + (-3.26)^2}$

5. Sep 8, 2015

### 0btuse

i emailed the professor and it appears there was an error in that it was forcing significant digits.