# C3 Implicit Differentiation HelpWatch

Announcements
Thread starter 3 years ago
#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
0
reply
3 years ago
#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.
0
reply
3 years ago
#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
0
reply
3 years ago
#4
xy =======> x*dy/dx + y*1
0
reply
Thread starter 3 years ago
#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
1
reply
3 years ago
#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?
0
reply
3 years ago
#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)
0
reply
3 years ago
#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 .
0
reply
3 years ago
#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.
0
reply
3 years ago
#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
0
reply
X

Write a reply...
Reply
new posts
Latest
My Feed

### Oops, nobody has postedin the last few hours.

Why not re-start the conversation?

see more

### See more of what you like onThe Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

### University open days

• University of West London
Postgraduate Open Day - Ealing Site Postgraduate
Thu, 20 Jun '19
• University of Warwick
Undergraduate Open Day Undergraduate
Fri, 21 Jun '19
• University of Bath
Find out about life at the University and discover our diverse range of Undergraduate courses. Our course areas include the Sciences, Humanities & Social Sciences, Engineering & Design, and Management. Undergraduate
Fri, 21 Jun '19

### Poll

Join the discussion

#### How did your AQA A-level Chemistry Paper 3 go?

Loved the paper - Feeling positive (256)
32.16%
The paper was reasonable (389)
48.87%
Not feeling great about that exam... (89)
11.18%
It was TERRIBLE (62)
7.79%

View All
Latest
My Feed

### Oops, nobody has postedin the last few hours.

Why not re-start the conversation?

### See more of what you like onThe Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.