sum on unit vectors...help!!

If a,b,c,d are unit vectors such that

(a x b) . (c x d) =1 and

a . c=1/2.....then

A) a,b,c are non coplanar
B) b,c,d are non coplanar
C) b,d are non parallel
D) a,d are parallel and b,c are parallel

1 Answers

its quite simple.

say axb=k

and cxd=h

now, k.h=1...

so |k|=|h|=1 and they are parallel

as |k|=1, a and b have an angle of pi/2

similarly c and d also have an angle of pi/2

as their cross products are parallel, they lie on same plane..

ans is A,B..

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