MathDB
black area by 6 arcs of radius = circle radius (1995 Chile Level 2 P2)

Source:

August 29, 2019
geometryarcareascircle

Problem Statement

In a circle of radius 11, six arcs of radius 11 are drawn, which cut the circle as in the figure. Determine the black area. https://cdn.artofproblemsolving.com/attachments/8/9/0323935be8406ea0c452b3c8417a8148c977e3.jpg