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Question
For a G.P. a = 2, r = `-2/3`, find S6
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Solution
a = 2, r = `-2/3`
Sn = `("a"(1 - "r"^"n"))/(1 - "r")`, for r < 1
S6 = `(2[1 - (-2/3)^6])/(1 - (-2/3)`
= `(2[1 - (2/3)^6])/(5/3)`
= `6/5[(729 - 64)/3^6]`
= `6/5[665/729]`
S6 = `266/243`
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