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प्रश्न
Answer the following:
Find the sum of the first 5 terms of the G.P. whose first term is 1 and common ratio is `2/3`
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उत्तर
The sum of first n terms of a G.P. is given by
Sn = `("a"(1 - "r"^"n"))/(1 - "r")`, if r < 1
Here, a = 1, r = `2/3`
∴ sum of first 5 terms of the G.P.
= S5 = `("a"(1 - "r"^5))/(1 - "r")`
= `(1[1 - (2/3)^5])/(1 - (2/3))`
= `(1 - 32/243)/((1/3))`
= `211/243 xx 3`
= `211/81`
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