Let a vector a has magnitude 9. Let a vector b be such that for every (x, y) R R − (0, 0) , the vector (x a + y b ) is perpendicular to the vector (6y a - 18x b ). Then the value of | a b | is equal to -

JEE Main 2022 Mathematics question

Let a vector has magnitude 9. Let a vector be such that for every (x, y) − {(0, 0)}, the vector is perpendicular to the vector . Then the value of is equal to -

(A)
(B)Correct
(C)9
(D)81

Answer: (B)

Solution

for all x, y. So the coefficients of xy, and must vanish: \vec{a}$|^{2} =

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Question ID VK-034781