Finding the area of crosssections

Question

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Let the radious of the circle is r. Now if i want to find out the area of the crosssection ( mentioned by red color) then how to proceed?

I have editted. Check please – user2378 Nov 02 '13 at 17:05 — user2378, Nov 02 '13 at 17:05

score 2 · Answer 1 · answered Nov 02 '13 at 17:03

Calculate the area of the circe with center O.
Calculate the area of the section PMN, when M and N are the intersections between the two circles. This can be done by firstly calculation the angle MPO.
substruct the results.

EDIT:

The calculation of angle MPO is done by observing triangle POM is a equilateral triangle.

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