Suppose that two circles of equal radius are drawn within a square such that each is centered on the same diagonal of the square and each is tangent to precisely two sides of the square, as well as to one another at precisely one point.
Next, on each end of the other diagonal, circles are drawn such they are both tangent at precisely one point to each of the two previously drawn circles and tangent to two sides of the square.
Let S be the ratio of the combined areas of the four circles to the area of the square. Find S to the nearest 3 decimal points.
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I am using IMGUR since there is no upload here. Can you please inform me how you get your sketches ? Thanks.
I am using IMGUR since there is no upload here. Can you please inform me how you get your sketches ? Thanks.
EP in small sketch should be
2
R
ABCD is the square, AD the top side. F the center of the First blue circle. FG its vertical radius = R, FE its horizontal radius. K the center of the last green circle. KH its vertical radius = r..... O is the intersection point of the diagonals and also the point of contact of the first two circles. Horizontal OP meets DC at P. Draw KL parallel to AD to meet FG at L.
Since it is the ratio, no generality is lost by assuming that the area of the square is 1 unit. So the side of the square =1 unit.
D
E
=
R
.
E
P
=
2
F
O
=
2
R
.
.
∴
2
1
=
D
P
=
R
+
2
R
⟹
R
=
2
+
2
1
.
.
.
.
(
1
)
L
F
=
F
G
−
L
F
=
R
−
r
.
.
.
K
L
=
H
G
=
1
−
R
−
r
.
.
.
F
K
=
R
+
r
.
I
n
r
t
∠
△
K
L
F
,
F
K
2
=
K
L
2
+
L
F
2
.
⟹
(
R
+
r
)
2
=
(
1
−
R
−
r
)
2
+
(
R
−
r
)
2
⟹
r
2
−
2
r
(
1
+
R
)
+
(
R
−
1
)
2
=
0
.
.
.
S
o
l
v
i
n
g
t
h
e
q
u
a
d
r
a
t
i
c
w
i
t
h
+
s
i
g
n
,
.
.
.
r
=
1
+
R
−
2
R
.
.
.
.
.
.
.
.
.
(
2
)
F
r
o
m
(
1
)
a
n
d
(
2
)
C
i
r
c
l
e
a
r
e
a
=
2
∗
π
∗
(
R
2
+
r
2
)
=
0
.
8
1
7
.
Since the square area is 1, this is the ratio.
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Let the side of the square be a , the radius of first and second two circles mentioned by r 1 and r 2 respectively.
Then we notice that for the diagonal the first two circles are on:
2 a = 2 ( r 1 + 2 r 1 ) ⇒ r 1 = 2 ( 1 + 2 ) 2 a = ( 1 − 2 1 ) a
On the other diagonal, half of it is given by:
( r 1 + r 2 ) 2 − r 1 2 + 2 r 2 = 2 2 a
⇒ ( r 1 + r 2 ) 2 − r 1 2 = 2 a − 2 r 2
⇒ r 1 2 + 2 r 1 r 2 + r 2 2 − r 1 2 = 2 a 2 − 2 a r 2 + 2 r 2 2
⇒ r 2 2 − 2 ( a + r 1 ) r 2 + 2 a 2 = 0 ⇒ r 2 2 − 2 ( 1 + 1 − 2 1 ) a r 2 + 2 a 2 = 0
⇒ r 2 2 − 2 ( 2 − 2 1 ) a r 2 + 2 a 2 = 0 ⇒ r 2 2 − ( 4 − 2 ) a r 2 + 2 a 2 = 0
⇒ r 2 = ( 2 − 2 1 − 4 − 2 2 ) a
⇒ S = a 2 2 π ( r 1 2 + r 2 2 ) = a 2 2 p i ( 0 . 2 9 2 9 2 + 0 . 2 1 0 5 2 ) a 2 = 0 . 8 1 7 4