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Given $2x^2 + y^2 = 4$, find $y''$. I found the first derivative which is $y' =$ ${-2x}\over y$.

I then got to $2(xy' - y)\over y^2$ and I don't know where to go from there.

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    Plug in the first derivative you've found.2012-10-19
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    so $2({{-2x^2}\over y} - y)\over y^2$?2012-10-19
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    Yep, although you may want to simplify the expression.2012-10-19
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    How can I simplify it?2012-10-19
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    The same way you'd do with any fraction. Just be careful so you don't multiply or divide by $0$.2012-10-19
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    When you simplify by bringing your top to the common denominator $y$, you may want to use the fact that $2x^2+y^2=4$.2012-10-19

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