Question

vector a = 2i - j + k, b = i + 2j - k, c = i + j - 2k. A vector coplanar with b and c,  whose projection on a  is of magnitude √(2/3) is

(A) 2i + 3j - 3k

(B) - 2i - j + k

(C) 2i + 3j + 3k

(D) 2i + j + 5k

Answer 1

Answer is (A) 2i + 3j - 3k

Let the required vector be vector r. Then