You are Here: Home >< Maths

# C3 Implicit Differentiation Help

Announcements Posted on
Why bother with a post grad? Are they even worth it? Have your say! 26-10-2016
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

## Register

Thanks for posting! You just need to create an account in order to submit the post
1. this can't be left blank
2. this can't be left blank
3. this can't be left blank

6 characters or longer with both numbers and letters is safer

4. this can't be left empty
1. Oops, you need to agree to our Ts&Cs to register

Updated: March 29, 2016
TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Today on TSR

### Who is getting a uni offer this half term?

Find out which unis are hot off the mark here

Poll
Useful resources

### Maths Forum posting guidelines

Not sure where to post? Read here first

### How to use LaTex

Writing equations the easy way

### Study habits of A* students

Top tips from students who have already aced their exams