Second derivative in terms of x and y?

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Homework Help Overview

The problem involves finding the second derivative \( y'' \) in terms of \( x \) and \( y \) from the equation \( y^2 + 2y = 2x + 1 \). The context is calculus, specifically dealing with implicit differentiation.

Discussion Character

  • Exploratory, Mathematical reasoning

Approaches and Questions Raised

  • Participants discuss the process of finding the first derivative and the subsequent steps needed to derive the second derivative. There is mention of substituting the first derivative into the equation for the second derivative.

Discussion Status

Some participants have provided guidance on how to proceed with taking the derivative of the first derivative. There is an indication that one participant believes they have arrived at a final answer, while others have not explicitly confirmed or questioned this outcome.

Contextual Notes

The original poster and another participant both express difficulty in moving beyond the first derivative, indicating a potential gap in understanding the subsequent steps required for the second derivative.

ObviousManiac
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Homework Statement



Find y" in terms of x and y:

y^2 + 2y = 2x + 1

Homework Equations



N/A

The Attempt at a Solution



I found the first derivative:

y^2 + 2y = 2x + 1
2yy'+2y'=2
2y'.(y+1)=2
y'=2/2(y+1)
y'=1/(y+1)

But I'm having trouble moving on from there.
 
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ObviousManiac said:

Homework Statement



Find y" in terms of x and y:

y^2 + 2y = 2x + 1

Homework Equations



N/A

The Attempt at a Solution



I found the first derivative:

y^2 + 2y = 2x + 1
2yy'+2y'=2
2y'.(y+1)=2
y'=2/2(y+1)
y'=1/(y+1)

But I'm having trouble moving on from there.
Now, take the derivative of y'.

Sure it will have y' in it, but then substitute the result you have for y' into that.
 
SammyS said:
Now, take the derivative of y'.

Sure it will have y' in it, but then substitute the result you have for y' into that.

alrighty so...

y" = derivative of 1/y+1

= (1)(y+1)^-1 ... then use product rule

= 0 + (-1(y+1)^-2)y' ... then plug in y'

= - [1/(y+1)]/(y+1)^2 ... combine

y" = - 1/(y+1)^3 final answer...

I think I did it right. Does this satisfy "in terms of x and y?"
 
Looks good !
 
thanks!
 

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