===== Arcus Tangens =====
==== Function ====
| @#FFBB00: definiendum | @#FFBB00: $\arctan: \{z\in\mathbb C\mid |z|\le 1, z\neq \pm i\}\to\mathbb C$ |
| @#FFBB00: definiendum | @#FFBB00: $\arctan(z):=\sum_{n=0}^\infty (-1)^n\frac{1}{2n+1} z^{2n+1} $ |

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=== Theorems ===
^ $\frac{{\mathrm d}}{{\mathrm d}z}\arctan(z)=\frac{1}{1+z^2}$ ^

=== References ===
Wikipedia: 
[[http://en.wikipedia.org/wiki/Inverse_trigonometric_functions|Inverse trigonometric functions]]

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=== Related ===
[[Exponential function]]