# A partial derivative Question

#### shikhar623

Joined May 9, 2009
31
I am doing an online assignment and struck at this question. Please explain how to do it.
Or better provide me the answer

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#### WBahn

Joined Mar 31, 2012
25,068
Or better yet, show YOUR work to get at an answer for YOUR assignment and then we can guide you through the problems you are making.

#### shikhar623

Joined May 9, 2009
31
Or better yet, show YOUR work to get at an answer for YOUR assignment and then we can guide you through the problems you are making.
It's an online assignment. There is no provision for the getting the answer. I have to either leave it or do it. Though the number of attempts are unlimited. Can you offer any help?

#### WBahn

Joined Mar 31, 2012
25,068
Yes, we can offer help AFTER you show your efforts to answer it yourself. Do the work as best you can and present it here. We can then look at what you have done and point out where you are going right and where you are going wrong. But YOU have to do the work.

#### shikhar623

Joined May 9, 2009
31
Yes, we can offer help AFTER you show your efforts to answer it yourself. Do the work as best you can and present it here. We can then look at what you have done and point out where you are going right and where you are going wrong. But YOU have to do the work.
Dx2/dudv = 4
Dy/dudv=3
At u=5 v=4

#### WBahn

Joined Mar 31, 2012
25,068
Dx2/dudv = 4
Dy/dudv=3
At u=5 v=4
How do you get these?

Start with what you want to know and then use the chain rule to expand it.

#### shikhar623

Joined May 9, 2009
31
I want partial derivative of Z wrt to v. But how to write it without knowing the actual expression of Z? I am missing some point here.

#### shikhar623

Joined May 9, 2009
31
How do you get these?

Start with what you want to know and then use the chain rule to expand it.
Please Correct me if i am wrong.

#### WBahn

Joined Mar 31, 2012
25,068
I want partial derivative of Z wrt to v. But how to write it without knowing the actual expression of Z? I am missing some point here.
You have

$$z \; = \; f(x,y)$$

and you want

$$\frac{\partial z}{\partial v} \; = \; \frac{\partial f(x,y)}{\partial v}$$

So what does the chain rule say about this in terms of the partial derivatives of f(x,y) with respect to x and y?

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#### shikhar623

Joined May 9, 2009
31
You have

$$z \; = \; f(x,y)$$

and you want

$$\frac{\partial z}{\partial v} \; = \; \frac{\partial f(x,y)}{\partial v}$$

So what does the chain rule say about this in terms of the partial derivatives of f(x,y) with respect to x and y?
Thank you. I did it, but the time had lapsed.

#### WBahn

Joined Mar 31, 2012
25,068
So what did you get for the answer?