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# C3 Implicit Differentiation Help Watch

1. Hi.
I am doing a C3 paper (link: http://www.mei.org.uk/files/papers/c308ju_fg48.pdf)

Anyway, i am stuck on Q7. I am ok with the method of implicit differentiation. Differentiate x terms and y terms, and stick a dy/dx after the y terms. Then you rearrange etc. However, i am slightly confused when on the part where i need to differentiate xy. I would use the product rule, however, when using the product rule, im unsure where the dy/dx goes

so i have x^2 + xy+y^2=12
i would do 2x+x+y(dy/dx)+2y(dy/dx)=0
but this is wrong
Help??
thanks
2. You have differentiated xy wrtx wrongly I'm afraid.

Do you see why that's the case?

Can you do the next step?

Also, moved to maths.
3. (Original post by starwarsjedi123)
Hi.
I am doing a C3 paper (link: http://www.mei.org.uk/files/papers/c308ju_fg48.pdf)

Anyway, i am stuck on Q7. I am ok with the method of implicit differentiation. Differentiate x terms and y terms, and stick a dy/dx after the y terms. Then you rearrange etc. However, i am slightly confused when on the part where i need to differentiate xy. I would use the product rule, however, when using the product rule, im unsure where the dy/dx goes

so i have x^2 + xy+y^2=12
i would do 2x+x+y(dy/dx)+2y(dy/dx)=0
but this is wrong
Help??
thanks
Look at this bit again

Kvothe's explained for me
4. xy =======> x*dy/dx + y*1
5. (Original post by Serine Soul)
Look at this bit again

aaaah ok i understand. i didnt really fully understand 'why' i was doing what i was. Thanks kvoothe
6. (Original post by starwarsjedi123)
Ok. i have differentiated 'xy' using the product rule, which gives me x+y.
Surely i stick the dy/dx after the y???
Have you looked at my post?

You don't just stick dy/dx infront of a variable.

(Original post by Kvothe the arcane)

Do you see why that's the case?

Can you do the next step?
7. (Original post by starwarsjedi123)
Ok. i have differentiated 'xy' using the product rule, which gives me x+y.
Surely i stick the dy/dx after the y???
So with implicit differentiation, when you used the product rule, dy/dx of y alone will simply be dy/dx (1)
8. (Original post by starwarsjedi123)
Ok. i have differentiated 'xy' using the product rule, which gives me x+y.
Surely i stick the dy/dx after the y???
Do you know how the product rule works? .

We also have that .
9. (Original post by Serine Soul)
So with implicit differentiation, when you used the product rule, dy/dx of y alone will simply be dy/dx (1)
Might want to be careful there, it's of - the derivative is an operator.
10. (Original post by Zacken)
Might want to be careful there, it's of - the derivative is an operator.
Lol alright

I can't explain math online

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