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Question
For a G.P., if a = 2, r = 3, Sn = 242, find n.
Solution
a = 2, r = 3, Sn = 242
Sn = `"a"(("r"^"n" - 1)/("r" - 1))`, for r > 1
∴ 242 = `2((3^"n" - 1)/(3 - 1))`
∴ 242 = 3n – 1
∴ 3n = 243
∴ 3n = 35
∴ n = 5.
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