diff --git a/maths/arc_length.py b/maths/arc_length.py
index 4c518f321dc7..90c200fc5291 100644
--- a/maths/arc_length.py
+++ b/maths/arc_length.py
@@ -1,17 +1,50 @@
 from math import pi
 
 
-def arc_length(angle: int, radius: int) -> float:
+def arc_length(angle: float, radius: float) -> float:
     """
+    Calculate the arc length of a circle.
+
+    The arc length is the distance along the curved line making up the arc.
+    Formula: arc_length = 2 * pi * radius * (angle / 360)
+    Wikipedia: https://en.wikipedia.org/wiki/Arc_length
+
+    Args:
+        angle: The angle in degrees
+        radius: The radius of the circle
+
+    Returns:
+        The arc length as a float
+
     >>> arc_length(45, 5)
     3.9269908169872414
     >>> arc_length(120, 15)
     31.415926535897928
     >>> arc_length(90, 10)
     15.707963267948966
+    >>> arc_length(0, 10)
+    0.0
+    >>> arc_length(360, 5)
+    31.41592653589793
+    >>> arc_length(180, 10)
+    31.41592653589793
+    >>> arc_length(45.5, 10.5)
+    8.33831050140291
+    >>> arc_length(-90, 10)
+    Traceback (most recent call last):
+        ...
+    ValueError: angle and radius must be positive
+    >>> arc_length(90, -10)
+    Traceback (most recent call last):
+        ...
+    ValueError: angle and radius must be positive
     """
+    if angle < 0 or radius < 0:
+        raise ValueError("angle and radius must be positive")
     return 2 * pi * radius * (angle / 360)
 
 
 if __name__ == "__main__":
-    print(arc_length(90, 10))
+    import doctest
+
+    doctest.testmod()