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# What are the magnitude and direction?

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## What are the magnitude and direction?

If a = (5, -12), what are the magnitude and direction of a?

The above question marked me wrong I answered:
(13, 292.6°)

I double checked this online and my answer was correct

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Originally Posted by csabin
If a = (5, -12), what are the magnitude and direction of a?

The above question marked me wrong I answered:
(13, 292.6°)

I double checked this online and my answer was correct
I calculated (13, 337deg). Here is what I have for the angle...270deg + 67deg = 337deg.

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Originally Posted by Uguessus
I calculated (13, 337deg). Here is what I have for the angle...270deg + 67deg = 337deg.

I even went back to a calculator website. The angle should be 360-67.3 = 292.7 degrees because if you think of this even logically the vector would have to be closer to the y axis much closer to 270 degrees. Due to the fact that -12 is much larger then 5.

Also you can even prove this with a calculation arctan(-12/5) = -67.3 degrees. I’m 1000% positive this is an error on test guide or I have wrote the problem wrong.

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You are right. I made a big mistake on where I should add or deduct the 67deg, 292Deg is right.

5. Originally Posted by Uguessus
You are right. I made a big mistake on where I should add or deduct the 67deg, 292Deg is right.
Always make a visual verification that you are in the right quadrant using the (X,Y) as a basis for your final answer.

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Originally Posted by Kalbi_Rob
Always make a visual verification that you are in the right quadrant using the (X,Y) as a basis for your final answer.
That's a good point. Thanks.

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