Let a , b and c be unit vectors such that a b is perpendicular to c . If is the angle between a and b , then which of the following is/are correct? 1. a b = , c 2. a ( b c )=0 Select the correct answer using the code given below.

NDA 2021 Mathematics question

Let , and be unit vectors such that is perpendicular to . If is the angle between and , then which of the following is/are correct? 1. 2. Select the correct answer using the code given below.

(A)1 only
(B)2 onlyCorrect
(C)Both 1 and 2
(D)Neither 1 nor 2

Answer: (B)

Solution

Statement 1: , where is the unit vector perpendicular to both and . It is given that is perpendicular to , so (when ) cannot be along ; thus

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Question ID VK-033677