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If ,  and  are three vectors in such a way that  and , then the value of  is equal to

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  1. 21
  2. -21
  3. 19

Answer (Detailed Solution Below)

Option 2 : -21
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Detailed Solution

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Concept:

The dot product of two vectors a and b is defined as:

where θ is the angle between vectors a and b.

Some properties of dot products of two vectors are as follows:

  • a.b = b.a (Commutative)

  • a.(b + c) = a.b + a.c (Distributive)

Given:

, 

Calculation:

We have 

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