Why is the domain of arctan power series |x|<=1?

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SUMMARY

The domain of the arctan power series is defined as |x| <= 1 due to its convergence properties, specifically linked to the integral of 1/(1+x^2). Unlike typical power series that converge for |x| < 1, the arctan series includes endpoints due to its behavior at these values. In contrast, the Taylor expansions of cosh(x) and sinh(x) converge for all x due to their entire function nature, which allows them to be defined across the entire complex plane.

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Why is the domain of arctan power series |x|<=1?
i understand why a power series has the domain |x|<1, but why is the power series of arctan |x|<=1?
thanks!

also, why are domains of the taylor expansions of coshx and sinhx: for all x?
 
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What do you know about the complex number plane?
 
are you kidding? arctan is the integral of 1/(1+x^2). what makes it look undefined at some points of |z| = 1?
 

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