took me a bit to Understand:
Step 1: Draw the 2 Intersection Points between the Circle and label them A and D, like in the picture above mine.
Step 2: Draw the following Radii = X:
-1- from Center - C1 of the Left Circle to Intersection Point A
-2- from Center -C1 of the Left Circle to Center- C2 of the Right Circle
-3- from Center - C1 of the Left Circle to Intersection Point D
if you label all the Radii = X, you will see that the Diamond Shape in the middle is composed of TWO Equilateral Triangles of Side = X
Step 3: Find Area of Shaded Region:
(1st) Focusing on the Sector Area of the Left Circle. The Central Angle created at Center - C1 with Line Segments X connected to Point A and Point D ----> is a 120 Degree Central Angle.
The Sector Area of this will include the Diamond in the Middle + the Outer Portions OUTSIDE the Diamond but INSIDE Circle A
2nd) Do the Same from the Perspective of the Right Circle. Again, you have the same 120 Degree Central Angle.
This Sector Area will include the Diamond AGAIN in the Middle + the Outer Portions OUTSIDE the Diamond but INSIDE Circle B
3rd) ADD these 2 Equivalent Sector Areas.
This will account for ALL of the Shaded Region. BUT --- we Actually included the DIAMOND AREA TWICE ---- we DOUBLE-COUNTED this Diamond Area
To make up for this Over-Counting, we need to Subtract ONE Area of the DIAMOND Region from the Addition.
Summary:
Area of Shaded Region = 2 * [Sector Area with 120 deg. Central Angle] - [Area of Diamond]
I. Sector Area with 120 deg. Central Angle. Radius = X
(120/360) * (pi) * (X)^2 = (1/3) * (pi) * (X)^2
again, we want to ADD Another to get the entire Region (with the Double-Counted Diamond)
2 * (1/3) * (pi) * (X)^2---- (equation 1)
II. Now, we need to SUBTRACT the Diamond Area to avoid the Double-Counting
the Diamond is composed of 2 Equilateral Triangles with Side = Radius = X
2 * [ (X)^2 * sqrt(3)] / 4 =
1/2 * (X)^2 * sqrt(3) ----- (equation 2)
III. Subtract (equation 2) FROM (equation 1) to get the Correct Area of the Shaded Region
[ 2 * (1/3) * (pi) * (X)^2 ] - [ 1/2 * (X)^2 * sqrt(3) ]
----LCD = 6-----
[(4/6) * (pi) * (X)^2 ] - [(3/6) * (X)^2 * sqrt(3) ]
----take (X)^2 as a Common Factor)
(X)^2 * [ (4 * (pi) - 3 * sqrt(3) / 6]
Answer -C-
I hope it didn't confuse anyone anymore and helped in some little way