If $f(z)$ is an entire function such that $ \lim_{x \rightarrow -\infty}\frac{f(x)}{|f(x)|}=1$ where $|f(x)|$ is the modulus of $f$, and $f(x)$ is just evaluating $f$ at real $x$. What can we say about $f(x)$ (or $f(z)$)?
Limit at infinity of a complex function
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complex-analysis
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9Not much. It could be the exponential function, or an even-degree polynomial with positive real leading coefficient, or $\cos z+2$, or $1/\Gamma(-z)$, or ... – 2011-10-24