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## Homework Statement

Ok so this satellite is orbiting the earth. The position vector is r = -0.707i + 0.707j + 0k and velocity vector is v = 0i + 0.5j + 0k. To find Vo (the angle between vector n and e), my book said the formula to use is arccos{(e dot r)/(|e||r|)}. However, I got 98 degree by using this formula while the correct answer is 173 degree.

## Homework Equations

arccos{(e dot r)/(|e||r|)}

## The Attempt at a Solution

I got the e vector as -.5304i-0.707j+0k, and therefore |e|=-.3535

r vector was given as -0.707i+0.707j+0k, and so |r|=0.9998

"e dot r" = -0.125 and "|e||r|" = 0.884

so arccos{(e dot r)/(|e||r|)} = 98 degree, which does not match the correct answer.

This is from the textbook "Fundamentals of Astrodynamics" problem 2.2 on P.114

http://aeroden.files.wordpress.com/2011/12/fundamentals_of_astrodynamics.pdf [Broken]

Thank you so much.

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