In the above diagram square A B C D is tangent to the circle at point P and vertices C and D are on the circle.
Let A R be the area of the red regions. If A A B C D A R = p α − β arcsin ( ω λ ) , where α , β , λ , ω , and p are coprime positive integers, find α + β + λ + ω + p .
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Nice one! When you use the tangent-secant theorem (first line), I believe it should be B E ⋅ B C , not B E ⋅ B D .
Let a be a side of square A B C D .
△ C O D is an isosceles triangle ⟹ O Q is the perpendicular bisector of base C D ⟹
C Q = Q D = 2 a
In right △ C O Q we have r 2 = a 2 − 2 a r + r 2 + 4 a 2 ⟹ a ( 5 a − 8 r ) = 0
and a = 0 ⟹ r = 8 5 a
B M = a − 2 ( a − r ) = 2 r − a = 4 a and sin ( θ ) = 2 r a = 5 4 ⟹
Area of sector M O P is A s = 2 1 θ r 2 = 2 1 arcsin ( 5 4 ) ( 6 4 2 5 ) a 2 = 1 2 8 2 5 arcsin ( 5 4 ) a 2
and
Area of trapezoid P B M O is A P B M O = 2 1 ( r + B M ) ( 2 a ) = 2 1 ( 8 5 a + 4 a ) ( 2 a ) = 3 2 7 a 2
⟹ A R = 2 ( A P B M O − A s ) = 2 ( 3 2 7 − 1 2 8 2 5 arcsin ( 5 4 ) ) a 2 =
( 6 4 2 8 − 2 5 arcsin ( 5 4 ) ) a 2 ⟹ A A B C D A R = 6 4 2 8 − 2 5 arcsin ( 5 4 ) = p α − β arcsin ( ω λ )
⟹ α + β + λ + ω + p = 1 2 6 .
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Let the side length of square A B C D be 1 Then the area of square A B C D , [ A B C D ] = 1 . Let B E = x . By tangent-secant theorem , we have B E ⋅ B C = B P 2 ⟹ x ⋅ 1 = ( 2 1 ) 2 ⟹ x = 4 1
Due to symmetry, we note that B E = P G = H Q = 4 1 . Since the diameter of the circle P Q = P H + H Q = 1 + 4 1 = 4 5 , the radius of the circle r = 8 5 .
Then the area of the red regions
A R = [ A B E F ] r e c t a n g l e − [ E P F G ] s e g m e n t = [ A B E F ] r e c t a n g l e − ( [ E P F O ] s e c t o r − [ E F O ] t r i a n g l e ) = A F ⋅ A B − r 2 sin − 1 ( O E E G ) + 2 1 ⋅ E F ⋅ O G = 1 ⋅ 4 1 − 8 2 5 2 sin − 1 ( 2 1 ⋅ 5 8 ) + 2 1 ⋅ 1 ⋅ ( 8 5 − 4 1 ) = 4 1 − 6 4 2 5 sin − 1 ( 5 4 ) + 1 6 3 = 6 4 2 8 − 2 5 sin − 1 ( 5 4 )
Since [ A B C D ] = 1 , [ A B C D ] A R = A R and the required answer is 2 8 + 2 5 + 4 + 5 + 6 4 = 1 2 6 .