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# C3 Chain Rule

1. Came across this question and my solution is different from the textbook answer.
The curve C is defined by the equation:

Show that there is only one stationary point and find its coordinates.

I used chain rule then found dy/dx to be:

When I set this equal to 0 I proved there was one stationary point but my x-coordinate was 1/3 when the book had 2/3.

Where have I went wrong?
2. (Original post by ozmo19)
Came across this question and my solution is different from the textbook answer.
The curve C is defined by the equation:

Show that there is only one stationary point and find its coordinates.

I used chain rule then found dy/dx to be:

When I set this equal to 0 I proved there was one stationary point but my x-coordinate was 1/3 when the book had 2/3.

Where have I went wrong?

1/( 1 - x ) 3 = 8/(x)3

cube root both sides... 1/( 1 - x ) = 2/(x)

*now rearrange & solve to get the book answer*
3. (Original post by the bear)

1/( 1 - x ) 3 = 8/(x)3

cube root both sides... 1/( 1 - x ) = 2/(x)

*now rearrange & solve to get the book answer*
1/( 1 - x ) 3 = 1/8(x)3 by accident.

Thank you!
4. (Original post by ozmo19)
1/( 1 - x ) 3 = 1/8(x)3 by accident.

Thank you!
we are here to help *
5. (Original post by the bear)
we are here to help *

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6. A: it is a product rule with a little bit of chain too...

u = e-x

v = 4e2x - 2ex

remember eax differentiates to aeax...

B: alternatively you could multiply out the brackets then you would not need the product rule ...
7. (Original post by the bear)
A: it is a product rule with a little bit of chain too...

u = e-x

v = 4e2x - 2ex

remember eax differentiates to aeax...

B: alternatively you could multiply out the brackets then you would not need the product rule ...
Took du/dx as e^-x and not -e^-x - Thanks for the reminder

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