1. Jun 17, 2016 #1

   funlord

   

   I can's understand the fact about the equation
   
   i cant prove the equation from the first attachment to the second attachment pls help.
   
   Sorry for bad english

    

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   funlord, Jun 17, 2016
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3. Jun 17, 2016 #2

   andrewkirk

   

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   The second last formula is ##\frac{dx}{dy}\frac d{dx}\left(\frac{dy}{dx}\right)^{-1}##.
   If we write ##y'## for ##\frac{dy}{dx}## then that is
   $$\frac1{y'}\frac d{dx}\left(\frac 1{y'}\right)$$
   What happens when you perform the differentiation?

    

   andrewkirk, Jun 17, 2016
4. Jun 17, 2016 #3

   funlord

   

   Thank you very much, I can understand now why it has a negative sign

    

   funlord, Jun 17, 2016

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