# partial derivatives

I need to do a series expansion of this forumla $$z = \sqrt{\frac{x+1}{y+1}}.$$

I need to get Zx Zxx and so on. but I really dont know where to start with this this.

just a push in the right direction should be enough.

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Pretend that y is just a constant, and differentiate like you would normally do. –  Unreasonable Sin Oct 27 '10 at 17:09
Is it homework? If so you should use the <homework> tag. –  AD. Oct 27 '10 at 18:22
It isn't directly homework. As in this is extra work not part of my course. –  PhilCK Oct 30 '10 at 12:10
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## 1 Answer

If you know how to differentiate already, remember that partial differentiation with respect to a certain independent variable treats the other independent variables as constants.

To use $(x+y)^2$ as an example, $\partial_x (x+y)^2$ is just $2(x+y)$ (chain rule). Now try this operation on your function.

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Thanks i got it. –  PhilCK Oct 30 '10 at 12:11
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