Proof.
The function
is entire, whence by the fundamental theorem
of complex analysis we have
(1) |
(2) |
For handling , we use the substitution
Using also de Moivre's formula we can write
Comparing the graph of the function with the line through the points and allows us to estimate downwards:
Hence we obtain
and moreover
Therefore
Then make to the substitution
It yields
(3) |
So we get also the result , Q.E.D.
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