In the diagram above points and are collinear, point lies on
and point lies on and and
Let be the perimeter of and be the area of .
If the value of for which can be expressed as
, where and are coprime positive integers, find .
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First we need to obtain θ to get the measure of the desired angles to obtain the area and perimeter.
m ∠ E C D = 1 8 0 ∘ − 2 θ , m ∠ E C B = 2 θ − 6 0 ∘ , m ∠ B E C = 3 0 0 ∘ − 4 θ
m ∠ A B E = 2 4 0 ∘ − 2 θ , m ∠ A E B = 3 θ − 1 2 0 ∘ and m ∠ A = 6 0 ∘ − θ ⟹
6 0 ∘ − θ = 3 θ − 1 2 0 ∘ ⟹ θ = 4 5 ∘ ⟹ m ∠ E C D = 9 0 ∘
and m ∠ A = m ∠ A E B = 1 5 ∘ ⟹ m ∠ A B E = 1 5 0 ∘
△ E C D is a ( 4 5 ∘ , 4 5 ∘ , 9 0 ∘ ) triangle ⟹ E D = 2 a
and in △ A B E :
A E 2 = 2 a 2 ( 1 − cos ( 1 5 0 ∘ ) = 4 a 2 sin 2 ( 7 5 ∘ ) ⟹ A E = 2 a sin ( 7 5 ∘ ) = 2 3 + 1 a
⟹ A D = A E + E D = 2 3 + 3 a and h = a sin ( 4 5 ∘ ) = 2 a ⟹
A △ A C D = 4 3 + 3 a 2
For P △ E B C :
B C 2 = 2 a 2 ( 1 − cos ( 1 2 0 ∘ ) = 4 a 2 sin 2 ( 6 0 ∘ ) ⟹ B C = 2 a sin ( 6 0 ∘ ) = 3 a
and B E = E C = a ⟹ P △ E B C = ( 3 + 2 ) a
A △ A C D + P △ E B C = 1 ⟹ ( 3 + 3 ) a 2 + 4 ( 3 + 2 ) a − 4 = 0 ⟹
dropping the negative root we have:
a = 3 + 3 2 ( − ( 3 + 2 ) + 5 ( 3 + 2 ) ) = 6 2 ( − 3 − ( 3 ) + 3 0 ( 2 − 3 ) ( 2 + 3 ) )
= 3 3 0 − 3 − 3 = 3 3 ∗ 1 0 − 3 − 3 = α α ∗ β − α − α ⟹
α + β = 1 3 .