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प्रश्न
For a G.P., if a = 2, r = `-2/3`, find S6.
उत्तर
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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