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Let k ˆ a j ˆ a i ˆ a a 3 2 1 + + = r a i > 0, i = 1, 2, 3 be vector which makes equal angles with the coordinate axes OX, OY and OZ. Also, let the projection of a r on the vector j ˆ 4 i ˆ 3 + be 7. Let b r be a vector obtained by rotating a r with 90°. If a r , b r and x-axis are coplanar, then projection of a vector b r on j ˆ 4 i ˆ 3 + is equal to :

1. 7
2. 2
3. 2
4. 4

Correct answer: 2

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