Which of the following function is NOITan entire function. A. Ln(z) B. e^{z^{2}} C cosz D. z^{3}+5z
Part A
ln(z)=ln(zeiθ)\ln(z) = \ln(ze^{i \theta})\\ln(z)=ln(zeiθ)
This is an entire function
Part B
ez2=∑n=0∞(znn!)2e^{z^{2}} = \sum_{n=0}^{\infin}(\frac{z^n}{n!})^2\\ez2=∑n=0∞(n!zn)2
Part C
cos(z)=eiz+e−iz2cos(z)= \frac{e^{i z}+e^{-i z}}{2}\\cos(z)=2eiz+e−iz
This is an entire function.
Part D
z3+5z=eiz+e−iz2=eiz+e−iz−2iz^3+5z = \frac{e^{i z}+e^{-i z}}{2}= \frac{e^{i z}+e^{-i z}}{-2i}\\\\z3+5z=2eiz+e−iz=−2ieiz+e−iz
This is NOT an entire function
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