absbara=absbarb=absbarc=1,(bara,barb)=al...

`absbara=absbarb=absbarc=1,(bara,barb)=alpha,(barb,barc)=beta(barc,bara) =gamma. " if "bara+barb+barc " is also a unit vector, then " cos alpha +cos beta +cos gamma`=

A

-1

B

3

C

-3

D

1

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A

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