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Write the Number of Vectors of Unit Length Perpendicular to Both the Vectors → a = 2 ^ I + ^ J + 2 ^ K and → B = ^ J + ^ K . - Mathematics

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Question

Write the number of vectors of unit length perpendicular to both the vectors \[\vec{a} = 2 \hat{ i } + \hat{ j }  + 2 \hat{ k }  \text{ and }  \vec{b} = \hat{ j }  + \hat{ k } \] .

 
Short/Brief Note
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Solution

Unit vectors perpendicular to \[\vec{a}\] and \[\vec{b}\]  are \[\pm \left( \frac{\vec{a} \times \vec{b}}{\left| \vec{a} \times \vec{b} \right|} \right)\] .

\[\vec{a} \times \vec{b} = \begin{vmatrix}\hat{ i }& \hat{ j }  & \hat{ k } \\ 2 & 1 & 2 \\ 0 & 1 & 1\end{vmatrix} = - \hat{ i }  - 2 \hat{ j } + 2 \hat{ k } \]
∴ Unit vectors perpendicular to \[\vec{a}\] and \[\vec{b}\]  are  \[\pm \frac{- \hat{ i } - 2 \hat{ j } + 2 \hat{ k } }{\sqrt{\left( - 1 \right)^2 + \left( - 2 \right)^2 + \left( 2 \right)^2}} = \pm \left( - \frac{1}{3} \hat{ i }  - \frac{2}{3} \hat{ j } + \frac{2}{3} \hat{ k } \right)\] 
Thus, there are two unit vectors perpendicular to the given vectors.
 
 
 
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Chapter 25: Vector or Cross Product - very short answers [Page 34]

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RD Sharma Mathematics [English] Class 12
Chapter 25 Vector or Cross Product
very short answers | Q 30 | Page 34

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