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Mathematics
Problem
The equations of four circles are
(
x
±
a
)
2
+
(
y
±
a
)
2
=
a
2
(x \pm a)^2 + (y \pm a)^2 = a^2
(
x
±
a
)
2
+
(
y
±
a
)
2
=
a
2
. The radius of a circle touching all the four circles is a.
(
2
−
1
)
a
(\sqrt{2} - 1)a
(
2
−
1
)
a
b.
2
2
a
2\sqrt{2}a
2
2
a
c.
(
2
+
1
)
a
(\sqrt{2} + 1)a
(
2
+
1
)
a
d.
(
2
+
2
)
a
(2 + \sqrt{2})a
(
2
+
2
)
a
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