My problem is to show that that where (lambda)>>(lambda_0) then Cauchy's Equation is an approximation of Sellmeier's.(adsbygoogle = window.adsbygoogle || []).push({});

Now I know generally how to solve it, but my trouble is in some of the expansions. The hint that is provided with the problem is "Write Sellmeier's Equation with only the first term in the sum; expand it by the binomial theorem; take the square root of n^2 and expand again."

it is the "expand by the binomial theorem" that gives me trouble. i looked up the binomial theorem and understand what it says but don't know how to apply it for the first expansion.

I'll try to attach some of my scratch work later, to clear up any confusion. thanks in advance for any help you can offer.

eric

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# Sellmeier's equation to cauchy's equation

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