The vector(s) which is/are coplanar with vectors i + j + 2 k and i + 2 j + k, and perpendicular to the vector i + j + k is/are

JEE Advanced Mathematics question

The vector(s) which is/are coplanar with vectors and , and perpendicular to the vector is/are

Answer: (A),(D)

Let . Then

r·( i + j + k) = x(1+1+2) + y(1+2+1) = 4(x+y) = 0 ⇒ y = -x,

r = x[( i + j + 2 k) - ( i + 2 j + k)] = x(- j + k).

So the required vectors are exactly the multi

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Question ID VK-110799