I wish to find out the area of a section of a ring which can be acted on my a rectangle 100mm wide by 60mm height. I know the inner diameter,ID and outer diameter,OD of the ring and the width of the ring $\frac{OD-ID}{2}$ will always be below 60mm so the ring will always be within the rectangle.
I thought it would be a simple take one section area away from the other... but it isn't.
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