If a,b,c are three unit vectors such that a+b+c is also unit vector and @,@2,@3 are angles  between vectors a,b; b,c and c,a respectively then among @,@2,@3

a) all r acute

b) all r 90

c) atleast one is acute

d) none of dis

The value of c so that for all real x, the vector (cxi + 6j + 3K), (xi  + 2j +2cxk) make an obtuse angle is

a) c<0

b) 0<c<4/3

c) -4/3<c<0

d) c>0

give the solution

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a and c are unit vectors and |b|=4. The angle between a and c is cos^-1 (1/4).  b-2c=xa. Find x.

A tetrahedrom has vertices at O(0,0,0), A(1,2,1), B(2,1,3) and C(-1,1,2). Then the angle between the faces OAB and ABC will be??

If i,j,k are unit orthonomal vectors and a is a vector such that a X r = j, then a.r is

a) o

b) 1

c) -1

d) arbitrary scalar..

Please give the method of solution

In a parallelogram ABCD, |AB|=a, |AD|=b, |AC|=c. The value of DB.AB is ?

a and c are unit vectors and |b|=4. The angle between a and c is sec (1/4).  b-2c=xa. Find x.