1.

If a and b are two unit vectors, then the vector (a + b) × (a × b) is parallel to A. (a − b) B. (a + b) C. (2a − b) D. (2a + b)

Answer»

Correct option   A. (a - b)

Explanation:

(a + b)× (a × b) = a ×(a × b) + a×(a × b) (a . b)a – (a .a)b + (b . b)a – (b.a)b a - b + a - b [a and b are unit vectors]

= 2 (a - b)

i.e., parallel to (a - b)



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