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Sep 27th 2009, 05:35 PM
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christina
Senior Member
Join Date: Sep 2009
Location: St. John's, NL
Posts: 124
angle..
Two vectors A and B have precisely equal magnitudes. For the magnitude of A + B to be 68 times greater than the magnitude of A  B, what must be the angle between them?
i ended up to cos1(4623/4625) but it says wrong answer.
help me out please
Sep 29th 2009, 04:29 AM
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physicsquest
Physics Team
Join Date: Feb 2009
Posts: 1,425
Try the cosine rule of vector addition
$\displaystyle
c^2\ =\ a^2\ +\ b^2\ \ 2\ a\ b\ cos\ \theta
$
where $\displaystyle \theta$ is the angle between them.
For a  b , use a + (b)
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