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Question
In a G.P., if t2 = 7, t4 = 1575, find r.
Solution
Given t2 = 7, t4 = 1575
tn = arn–1
∴ t2 = ar
∴ 7 = ar
a = `7/"r"` ...(i)
t4 = ar3
∴ ar3 = 1575
∴ `"r"^3 xx (7/"r")` = 1575 ...[From (i)]
∴ r2 x 7 = 1575
∴ r2 = `1575/7`
∴ r2 = 225
∴ r = ±15
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