Hmmm. . .the easiest way I can think of is to turn the circle into a polygon, clip using the rectangle, and then calculate the remaining area.

For example, if one circle represents every number between 1 and 25 and another represents every number between 1 and 100 that is divisible by 5, the overlapping area would contain the numbers 5 ...

Rotate a two-circle Venn diagram by 180 degrees (or a three-circle one by 120 degrees), and it looks the same. But the four-ellipse diagram doesn’t have rotational symmetry. Can that be fixed?

A new rose has blossomed in the garden of mathematics: a flowery Venn diagram for 11 sets of objects. Venn diagrams use overlapping circles to show all possible relationships between sets ...