Diagram 1:
Diagram 2:
Extend both diagrams above to an infinite number of circles.
(Diagram 1:) In equilateral , the largest circle is tangent to each side of and for circle is tangent to circle and to and .
Let be the total area of all the circles.
(Diagram 2:) For each integer , circle is tangent to and tangent to the line and the positive axis.
Let and be the total circumference and area of all the circles respectively.
If , where and are coprome positive integers, find .
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Using the above diagram we obtain:
a 1 2 R 1 = tan ( 3 0 ∘ ) = 3 1 ⟹ R 1 = 2 3 a 1
and H 2 = H 1 − 2 R 1 = 2 3 a 1 − 3 1 a 1 = 2 3 a 1
H 2 H 1 = 3 = a 2 a 1 ⟹ a 2 = 3 a 3
a 2 2 R 2 = 3 1 ⟹ R 2 = 2 3 a 2 = 6 3 a 1
H 3 = H 2 − 2 R 2 = 2 3 a 1 − 3 3 a 1 = 1 8 3 a 1 = 6 3 a 1
H 3 H 2 = 3 = a 3 a 2 ⟹ a 3 = 3 a 2 = 9 a 1 ⟹
a 3 2 R 3 = 3 1 ⟹ R 3 = 2 3 a 3 = 1 8 3 a 1
In General:
R n = 2 3 a 1 ( 3 1 ) n − 1
Note: H n = 2 3 a 1 ( 3 1 ) n − 2
⟹ A n = π R n 2 = 1 2 π ( 9 1 ) n − 1 a 1 2
⟹ S = ∑ n = 1 ∞ A n = 1 2 π a 1 2 ( 8 9 ) = 3 2 3 π a 1 2 = 4 3 ( 8 3 π ( 3 1 ) a 1 2 = 8 3 3 π A △ A B C = 8 3 π A △ A B C
⟹ A △ A B C S = 8 3 π .
Note: I'm using the same notation R n in Diagram 2 to denote different radii.
O w 0 = 4 + 2 2 R 1
△ O A 1 w 0 ∼ △ w 1 A 2 w 0 ⟹ R 1 4 + 2 2 R 1 = R 1 − R 2 R 1 + R 2 ⟹
( 4 + 2 2 − 1 ) R 1 = ( 4 + 2 2 + 1 ) R 2 ⟹ R 2 = 4 + 2 2 + 1 4 + 2 2 − 1 R 1
R 3 = 4 + 2 2 + 1 4 + 2 2 − 1 R 2 = ( 4 + 2 2 + 1 4 + 2 2 − 1 ) 2 R 1
In General: R n = ( 4 + 2 2 + 1 4 + 2 2 − 1 ) n − 1 R 1
⟹ A n = π R n 2 = π R 1 2 ( ( 4 + 2 2 + 1 4 + 2 2 − 1 ) 2 ) n − 1
⟹ A = ∑ n = 1 ∞ A n = π R 1 2 ∑ n = 1 ∞ ( ( 4 + 2 2 + 1 4 + 2 2 − 1 ) 2 ) n − 1
= 4 4 + 2 2 ( 4 + 2 2 + 1 ) 2 π R 1 2
and
C n = 2 π R n = 2 π R 1 ( 4 + 2 2 + 1 4 + 2 2 − 1 ) n − 1
⟹ C = ∑ n = 1 ∞ C n = 2 π R 1 ∑ n = 1 ∞ ( 4 + 2 2 + 1 4 + 2 2 − 1 ) n − 1 =
( 4 + 2 2 ) π R 1 ⟹ C 2 = ( 4 + 2 2 ) 2 π 2 R 1 2
⟹ C 2 A = 4 π 4 + 2 2 1
⟹ A △ A B C S ∗ C 2 A = 2 5 2 2 + 2 2 3 = β λ β β + β β α ⟹
α + β + λ = 1 0 .