Let a = a1i + a2j + a3k, ai > 0, i = 1,2,3 be a vector which makes equal angles with the axes OX, OY and OZ.

Question

Let \(\vec a = a_1\hat i + a_2\hat j + a_3\hat k\), a_i > 0, i = 1,2,3 be a vector which makes equal angles with the axes OX, OY and OZ. Also, let the projection of  \(\vec a\) on the vector \(3\hat i+4\hat j\) be 7. Let \(\vec b\)be a vector obtained by rotating \(\vec a\) with 90°. If \(\vec a,\vec b\) and x - axis are coplanar, then projection of a vector \(\vec b\) on \(3\hat i+4\hat j\) is equal to

(A) √7

(B) √2

(C) 2

(D) 7

Answer 1

Correct option is (B) √2