# Components using partial derivatives

here is the question:
http://i44.tinypic.com/xe53tc.gif

here is the solution:
http://i43.tinypic.com/2nuokfq.gif
my first question regarding this whole thing is.
why when the doing the partial derivative by "r" we dont multiply by minus
the formula says (minus derivative)
but all they do is making a derivative without multiplying by minus?

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tiny-tim
Homework Helper
Hi transgalactic!
here is the question:
http://i43.tinypic.com/2nuokfq.jpg

here is the solution:
http://i43.tinypic.com/2nuokfq.gif
erm … they're the same

get some sleep! :zzz:​
why when the doing the partial derivative by "r" we dont multiply by minus
the formula says (minus derivative)
but all they do is making a derivative without multiplying by minus?
?? but they have multiplied by the minus …

∂/∂r (1/r2) = -2/r3, and ∂/∂θ (cosθ) = -sinθ

but we are doing a derivative by 'r'(partial derivative)
we dont touch $$\theta$$ ,its constant

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i changed the original post
now its ok

tiny-tim
we dont touch $$\theta$$ ,its constant