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jesuslovesu

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## Homework Statement

[tex]\mathbf{r} = rsin(\theta)cos(\phi) \hat x + rsin(\theta)sin(\phi) \hat x + r cos(\theta) \hat z[/tex]

I am kind of following the description of the process given at http://mathworld.wolfram.com/SphericalCoordinates.html

I want to find [tex]\hat r[/tex] and I understand everything except:

Why is [tex]\hat r = \frac{\frac{d\mathbf{r}}{dr} }{|\frac{d\mathbf{r}}{dr}|} [/tex] (why the derivatives)?

Normally if I were going to find the unit vector I would just say the unit vector u hat = u/|u|

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