If a unit vector is represented by 0.5 i + 0.8 j + c k, the value of c is

 

The angle between A and B is theta. The value of the triple product A.(B X A) is

 The angle between A and B is theta. The value of the triple product A.(B X A) is 

The magnitudes of vectors A, B and C are 3,4 and 5 units respectively. If A + B = C , then the angle between A and B is

NEET 1988 

The magnitudes of vectors $\vec{A}, \vec{B} \; and \; \vec{C} $ are 3,4 and 5 units respectively. If $\vec{A} + \vec{B} = \vec{C}$ , then the angle between $\vec{A} \; and \; \vec{B}$ is

Pythagoras triplet $3^2 + 4^2 = 5^2$

So the angle will be $90^o$ between $\vec{A} \; and \; \vec{B}$