What is the Vector Identity for \vec A and \hat n?

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SUMMARY

The discussion focuses on the vector identity for an arbitrary vector \(\vec A\) and a unit vector \(\hat n\). It establishes that \(\vec A\) can be decomposed into two components: the projection of \(\vec A\) onto \(\hat n\), represented as \((\vec A \cdot \hat n)\hat n\), and the component orthogonal to \(\hat n\), derived using the Vector Triple Product Identity. The identity \(\left( {\vec A \times \vec B} \right) \times \vec C = -\vec A\left( {\vec B \cdot \vec C} \right) + \vec B\left( {\vec A \cdot \vec C} \right)\) is crucial for proving the orthogonal component. This decomposition illustrates how \(\vec A\) is expressed as the sum of its projections on the line defined by \(\hat n\) and its orthogonal complement.

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  • Understanding of vector notation and operations
  • Familiarity with unit vectors and their properties
  • Knowledge of the Vector Triple Product Identity
  • Concept of vector projections and orthogonal components
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Let [itex]\vec A[/itex] be an arbitrary vector and let [itex]\hat n[/itex] be a unit vector in some fixed direction. Show that
[tex]\vec A = (\vec A .\hat n)\hat n + (\hat n \times \vec A)\times \hat n.[/tex]
 
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You can use the Vector Triple Product Identity on the last term:

[tex]\left( {\vec A \times \vec B} \right) \times \vec C = - \vec A\left( {\vec B \cdot \vec C} \right) + \vec B\left( {\vec A \cdot \vec C} \right)[/tex]
 
The vector [tex]\vec A[/tex] is expressed as the sum of its projections on [tex]W= \mathcal{L} (\hat{n})[/tex] and [tex]W^\bot[/tex].

Prove that the two terms represent these.
 
Last edited:

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