In Right △ A B C , D C = 2 3 x , D E = 2 x , A F is perpendicular bisector of B D and D P is an arc of a circle with center at C .
Let A R 1 and A R 2 be the areas of the green and pink regions respectively.
If A R 2 A R 1 = β − β ( α − β ) ( α β − π ) , where α and β are coprime positive integers, find α + β .
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∠ A is a right angle and A F bisects B D ⟹ △ A B D is an isosceles right triangle
⟹ A D = a ⟹ B D = 2 a and △ A B C is a ( 3 0 , 6 0 , 9 0 ) triangle ⟹
A C = 2 3 x = 2 3 x + 2 a = 3 a ⟹ x = 3 2 ( 3 − 1 ) a = 3 2 ( 3 − 3 ) a ⟹
D E = 2 x = 3 3 − 3 a and h ∗ = E G = 2 x sin ( 4 5 ∘ ) = ( 3 3 − 3 ) ( 2 1 ) a ⟹
A △ D B E = A R 2 = ( 2 1 ) ( 2 a ) ( 3 3 − 3 ) ( 2 1 ) a = 6 3 − 3 a 2
and
A △ D E C = 8 3 x 2 = 8 3 ( 9 4 ) ( 1 2 − 6 3 ) a 2 = 9 3 3 ( 2 − 3 ) a 2 = 3 3 ( 2 − 3 ) a 2
and
r = 2 3 x = ( 3 − 1 ) a ⟹ the area of the sector A 1 = ( 2 1 ) ( 6 π ) ( 3 − 1 ) 2 a 2 =
1 2 π ( 4 − 2 3 ) a 2 = 6 π ( 2 − 3 ) a 2
⟹ A R 1 = A △ D E C − A 1 = ( 2 − 3 ) ( 6 2 3 − π ) a 2 ⟹
A R 2 A R 1 = 3 − 3 ( 2 − 3 ) ( 2 3 − π ) = β − β ( α − β ) ( α β − π )
⟹ α + β = 5 .
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Since D E = 2 1 x and D C = 2 3 x , ∠ E C D = 3 0 ° .
R 1 is the difference between △ C D E and sector C D P , so A R 1 = 2 1 ⋅ D C ⋅ D E − 3 6 0 ° 3 0 ° π D C 2 = 2 1 ⋅ 2 3 x ⋅ 2 1 x − 3 6 0 ° 3 0 ° π ( 2 3 x ) 2 = 1 6 1 ( 2 3 − π ) x 2 .
Since A F is the perpendicular bisector of B D and A B ⊥ A D , A B = A D .
Since △ A B C ∼ △ D E C by AA similarity, D C D E = A C A B . Letting a = A B = A C , 2 3 x 2 1 x = a + 2 3 x a , which solves to a = 4 1 ( 3 + 3 ) x .
That means A R 2 = 2 1 ⋅ D E ⋅ A D = 2 1 ⋅ 2 1 x ⋅ 4 1 ( 3 + 3 ) x = 1 6 1 ( 3 + 3 ) x 2 .
So A R 2 A R 1 = 1 6 1 ( 3 + 3 ) x 2 1 6 1 ( 2 3 − π ) x 2 = 3 + 3 2 3 − π = ( 3 − 3 ) 2 ( 3 + 3 ) ( 3 − 3 ) 2 ( 2 3 − π ) = 3 − 3 ( 2 − 3 ) ( 2 3 − π ) .
Therefore, α = 2 , β = 3 , and α + β = 5 .