The term "vesica piscis," meaning "fish bladder" in Latin, is used for the particular symmetric lens formed by the intersection of two equal circles whose centers are offset by a distance equal to the circle radii (Pedoe 1995, p. xii). The height of the lens is given by letting in the equation for a circle-circle intersection
(1)
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giving
(2)
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The vesica piscis therefore has two equilateral triangles inscribed in it as illustrated above.
The area of the vesica piscis is given by plugging into the circle-circle intersection area equation with ,
(3)
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giving
(4)
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(5)
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(OEIS A093731). Since each arc of the lens is precisely 1/3 of a circle, perimeter is given by
(6)
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Renaissance artists frequently surrounded images of Jesus with the vesica piscis (Pedoe 1995, p. xii; Rawles 1997).