Question about solution to Laplacian in Spherical Polars

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SUMMARY

The discussion focuses on deriving the solution to the Laplacian in spherical polar coordinates, specifically addressing the equations ##\lambda_{1} + \lambda_{2} = -1## and ##\lambda_{1}\lambda_{2} = -\lambda##. The equation under consideration is ## \frac{d^2S}{dt^2}+\frac{dS}{dt}-\lambda S=0 ##, with a proposed solution of the form ## S=e^{bt} ##. The roots of the resulting quadratic equation ## b^2+b-\lambda=0 ## are derived using the relationships from quadratic equations, confirming that the roots satisfy the established properties of sums and products.

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I was following this derivation of the solution to the Laplacian in spherical polars. I was wondering where the two equations ##\lambda_{1} + \lambda_{2} = -1## and ##\lambda_{1}\lambda_{2} = -\lambda## come from? Thanks.
 
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We want to solve the equation ## \frac{d^2S}{dt^2}+\frac{dS}{dt}-\lambda S=0 ##. So let's try a solution of the form ## S=e^{bt} ## (and find b), which gives ## b^2+b-\lambda=0 ##. But for any quadratic equation ## px^2+qx+r=0 ##, we know that the two roots satisfy ## x_1+x_2=-\frac{q}{p} ## and ##x_1x_2=\frac{r}{p}##.
 
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