In the above diagram, ∠ B C A ≅ ∠ E B D and A E = D C = x , B C = 6 x − 1 and E D = 2 x .
If the pink area A p = β α γ α ( ω + γ γ λ ) , where α , β , γ , ω and λ are coprime positive integers, find α + β + γ + ω + λ .
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AB² = BC² - AC²
= (6x - 1)² - (4x)²
= 20x² - 12x + 1
In the same way using Pythagoras, we get
BE² = 21x² - 12x + 1
(and
BD² = 29x² - 12x + 1
though not necessary)
Triangle BED is similar (not congruent, right?) to triangle CEB.
ED / BE = EB / CE
(ED)(CE) = BE²
6x² = 21x² - 12x + 1
15x² - 12x + 1 = 0
x = (2 ± √(7/3)) / 5
Since 6x - 1 > 0 ==> x > 1/6,
x = (2 + √(7/3)) / 5
Pink area
= x√(20x² - 12x + 1)
= √5 (19 + 2²√21) / ((3)(5²))
by substitution.
Answer
= 5 + 3 + 2 + 19 + 21
= 50
Let ∠ B C A = ∠ E B D = θ , ∠ A B E = α , and A B = h . By Pythagorean theorem ,
A B 2 h 2 = B C 2 − C A 2 = ( 6 x − 1 ) 2 + ( 4 x ) 2 = 2 0 x 2 − 1 2 x + 1
Consider tan ∠ A B D = tan ( α + θ ) ,
tan ( α + θ ) h 3 x h 3 x 9 x 2 5 x 2 1 5 x 2 − 1 2 x + 1 ⟹ x ⟹ A p = 1 − tan α tan θ tan α + tan θ = 1 − h x ⋅ 4 x h h x + 4 x h = 3 x h 4 x 2 + h 2 = 4 x 2 + h 2 = h 2 = 0 = 1 5 6 + 2 1 = 2 2 x ⋅ h = x h = 5 x 2 = 5 ( 1 5 6 + 2 1 ) 2 = 3 ⋅ 5 2 5 ( 1 9 ± 2 2 2 1 ) Note that tan α = A B A E = h x and tan θ = C A A B = 4 x h Note that h 2 = 2 0 x 2 − 1 2 x + 1 Since 6 x − 1 > 0 and h 2 = 5 x 2
Therefore the required answer is 5 + 3 + 2 + 1 9 + 2 1 = 5 0
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In △ E B D we have:
λ 1 + 1 8 0 − λ 3 + λ 2 = 1 8 0 ⟹ λ 3 = λ 1 + λ 2
and tan ( λ 3 ) = x h , tan ( λ 2 ) = 3 x h and tan ( λ 1 ) = 4 x h ⟹
tan ( λ 1 ) = 4 1 tan ( λ 3 ) = 4 1 tan ( λ 1 + λ 2 )
and
tan ( λ 2 ) = 3 1 tan ( λ 1 + λ 2 ) ⟹ 4 tan ( λ 1 ) = 3 tan ( λ 2 ) ⟹
tan ( λ 2 ) = 3 4 tan ( λ 1 ) and 4 tan ( λ 1 ) = tan ( λ 1 + λ 2 ) = 3 − 4 tan 2 ( λ 1 ) 7 tan ( λ 1 ) ⟹
tan ( λ 1 ) ( 1 6 tan 2 ( λ 1 ) − 5 ) = 0 and tan ( λ 1 ) = 0 ⟹ tan ( λ 1 ) = 4 5 ⟹
h = 4 x tan ( λ 1 ) = 5 x ⟹ 2 1 x 2 = 3 6 x 2 − 1 2 x + 1 in right △ A B C
⟹ 1 5 x 2 − 1 2 x + 1 = 0 ⟹ x = 1 5 6 ± 2 1 and x = 1 5 6 − 2 1 ⟹ 6 x − 1 < 0
∴ we choose x = 1 5 6 + 2 1 ⟹ h = 5 ( 1 5 6 + 2 1 ) ⟹
A p = x h = 5 ( 1 5 6 + 2 1 ) 2 = 3 ∗ 5 2 5 ( 1 9 + 2 2 2 1 ) =
β ∗ α γ α ( ω + γ γ λ ) ⟹ α + β + γ + ω + λ = 5 0 .