Let .
The length of the semi-major and semi-minor axis of the two congruent ellipses above are units and unit respectively.
If the centers of the two ellipses are unit apart and the area of the region can be expressed as , where and are coprime positive integers, find .
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I chose the ellipses ( a 2 x 2 + y 2 = 1 above the line y = 0 ) and ( a 2 x 2 + ( y − 1 ) 2 = 1 below the line y = 1 ) .
Solving for y in both ellipses we want:
f ( x ) = a 1 a 2 − x 2 and g ( x ) = 1 − a 1 a 2 − x 2 .
f ( x ) = g ( x ) ⟹ x = ± 2 3 a ⟹ the area A = ∫ − 2 3 a 2 3 a f ( x ) − g ( x ) d x = a 2 ∫ − 2 3 a 2 3 3 a a 2 − x 2 d x − 3 a
For I = a 2 ∫ − 2 3 a 2 3 a a 2 − x 2 d x
Let x = a sin ( θ ) ⟹ d x = a cos ( θ ) ⟹ I = 2 a ∫ − 3 π 3 π cos 2 ( θ ) d θ = a ∫ − 3 π 3 π 1 + cos ( 2 θ ) d θ = a ( θ + 2 1 sin ( 2 θ ) ) ∣ − 3 π 3 π = a ( 3 2 π + 2 3 ) ⟹ A = a ( 3 2 π − 2 3 ) = a ( β α π − α β ) ⟹ α + β = 5