Solving Tangent Plane Approximation in Einstein Gravity

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SUMMARY

The forum discussion focuses on the tangent plane approximation in Einstein gravity as described in Zee's "Einstein Gravity in a Nutshell," specifically in section I.6 on page 83. The approximation of the south pole of a sphere is analyzed, revealing that the first equation is approximated by a series expansion for the square root function, specifically ##\sqrt{1-a}##, where ##a=(x^2+y^2)/L^2##. The author neglects higher-order terms in ##a##, confirming that this method is a series approximation rather than a direct application of Leibniz's rule.

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Lapidus
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In Zee "Einstei gravity in a nutshell" section I.6, page 83, the author says about the approxiamtion of the south pole of sphere

pic1.PNG


How is the first equation approximated by the second? One page later he does this expansion again.

pic2.PNG

Is this thecalculus Leibnitz rule? Or some clever trick?

Thank you!
 
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It's the series approximation for ##\sqrt {1-a}##, with ##a=(x^2+y^2)/L^2##. He just neglects terms above first order in ##a##.
 
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