Implicit Differentiation of the second derivative.

jdx10n

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Apr 5, 2011
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I am able to find dy/dx, but when it comes to plugging in dy/dx and simplifying, I am completely lost.
Here is the problem...

x^3+y^3=1
 
Differentiate the second time. Then, sub in y' from the first derivative.

Here is an example:

x2+y2=1\displaystyle x^{2}+y^{2}=1

2x+2yy=0\displaystyle 2x+2yy'=0

y=xy\displaystyle y'=\frac{-x}{y}

Now, differentiate xy\displaystyle \frac{-x}{y} using the quotient rule.

y=y(1)(x)yy2\displaystyle y''=\frac{y(-1)-(-x)y'}{y^{2}}

Resub y' from the first time around:

y=y(x)(xyy’)y2\displaystyle y''=\frac{-y-(-x)(\overbrace{\frac{-x}{y}}^{\text{y'}})}{y^{2}}

y=x2y31y\displaystyle y''=\frac{-x^{2}}{y^{3}}-\frac{1}{y}

Apply this to your problem.
 
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