# Help me prove

1. Aug 1, 2005

### Reshma

Let $\vec A$ be an arbitrary vector and let $\hat n$ be a unit vector in some fixed direction. Show that
$$\vec A = (\vec A .\hat n)\hat n + (\hat n \times \vec A)\times \hat n.$$

2. Aug 1, 2005

### TD

You can use the Vector Triple Product Identity on the last term:

$$\left( {\vec A \times \vec B} \right) \times \vec C = - \vec A\left( {\vec B \cdot \vec C} \right) + \vec B\left( {\vec A \cdot \vec C} \right)$$

3. Aug 1, 2005

### Maxos

The vector $$\vec A$$ is expressed as the sum of its projections on $$W= \mathcal{L} (\hat{n})$$ and $$W^\bot$$.

Prove that the two terms represent these.

Last edited: Aug 1, 2005