Chain rule for denominator in second order derivatives

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SUMMARY

The discussion focuses on the application of the chain rule in transforming second-order derivatives, specifically from ##\frac{d^2x}{dy^2}## to ##\frac{d^2x}{dz^2}##. The correct formulation involves using the chain rule, represented as ##\frac{dx}{dz} = \frac{dx}{dy} \cdot \frac{dy}{dz}##, and applying the product rule to derive ##\frac{d^2x}{dz^2} = \frac{dx}{dy} \cdot \frac{d^2y}{dz^2} + \frac{d^2x}{dydz} \cdot \frac{dy}{dz}##. A correction was made regarding the second term, confirming it should be ##\frac{d^2x}{dydz}##.

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TL;DR
What is the chain rule for switching the denominator of a second order derivative?
Given ## \frac{d^2x}{dy^2} ##, what is the chain rule for transforming to ##\frac{d^2 x}{dz^2} ##?

(This is not a homework question)
 
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##dx/dz = dx/dy*dy/dz## (chain rule)
So
##d^2x/d^2z = dx/dy*d^2y/d^2z + d^2x/dydz*dy/dz## (product rule) (Corrected as @PeroK pointed out)
 
Last edited:
FactChecker said:
##dx/dz = dx/dy*dy/dz## (chain rule)
So
##d^2x/d^2z = dx/dy*d^2y/d^2z + d^2x/dxdz*dy/dz## (product rule)

You've got a typo there. The second term should be ##\frac{d^2x}{dydz}##.
 
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Great. Thanks so much!
 

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