Update arc_length.py (TheAlgorithms#8964)

* Update arc_length.py

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* Update arc_length.py

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* Update arc_length.py

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* Update arc_length.py

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Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

Author: Guduly

maths/arc_length.py

@@ -7,6 +7,8 @@ def arc_length(angle: int, radius: int) -> float:
     3.9269908169872414
     >>> arc_length(120, 15)
     31.415926535897928
+    >>> arc_length(90, 10)
+    15.707963267948966
     """
     return 2 * pi * radius * (angle / 360)