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regular smooth curve - Penn Math

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Tubes about circles in the plane.<br />

The simplest example is that of a tube of radius � about a<br />

circle of radius r in the plane, so just an annulus between<br />

concentric circles of radii r + � and r � � , with area<br />

� (r + �) 2 � � (r � �) 2 = � 4r� = (2�r) (2�)<br />

= (circumference of circle) (width of tube)<br />

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