The sum of the lengths of projections of p i + q j + r k on the co-ordinate axes, where p = 4, q = -5, r = 7 is

MHT CET 2022 Mathematics question

The sum of the lengths of projections of on the co-ordinate axes, where p = 4, q = -5, r = 7 is

(A)6 units
(B)16 unitsCorrect
(C)20 units
(D)28 units

Answer: (B)

Solution

The projection of on the x-, y-, z-axes are , , respectively (dot product with , , ). The question asks for the sum of the lengths of these projections, and a length

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Question ID VK-094023