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There are various ways of deriving . Here's one. And here's my version:So if we put is the root of the equation:
for which .
Noting that satisfies this equation, we can factorise:
and then discard the factor , since .
We then note that is also a root. Hence is a factor, which again we discard for the same reason; leaving us with the remaining factor:the positive root of which is:Hence