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Question

Let an be a G.P such that a4a6=14 and a2+a5=216. Then a1=

A
12 or 1087
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B
10
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C
7 or 547
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D
None of these
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Solution

The correct option is A 12 or 1087
Let a,ar,ar2,... be in G.P such that a4a6=14.
a1r3a1r5=14
a1r3a1r5=14
r=±2
Case (1): When r=2
a2+a5=216
a1r+a1r4=216
2a1+16a1=216
18a1=216
a1=12
Case (2): When r=2
a2+a5=216
a1r+a1r4=216
2a1+16a1=216
14a1=216
a1=21614
a1=1087

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