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Mathematics
Mathematics
Problem
State the necessary and sufficient condition for the infinite geometric series
a
+
a
r
+
a
r
2
+
⋯
a + ar + ar^2 + \cdots
a
+
a
r
+
a
r
2
+
⋯
to have a finite sum. a)
∣
r
∣
≤
1
|r|\le 1
∣
r
∣
≤
1
b)
∣
r
∣
<
1
|r|<1
∣
r
∣
<
1
c)
r
<
1
r<1
r
<
1
d)
0
<
r
<
1
0<r<1
0
<
r
<
1
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