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Find the least value of `n`for which the sum `1+3+3^2+ ton`terms is greater than 7000. |
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Answer» `1+3+3^2+...->n` terms Here, first term, `a = 1` and common ratio, `r = 3`. `:. S_n = (1(3^n-1))/(3-1)` `:. (3^n-1))/(3-1) gt 7000` `=>3^n -1 gt 14000` `=>3^n gt 14001` Now, `3^8 = 6561` `3^9 = 19683` So, minimum value of `n` for which `3^n` is greater than `14001` is `9`. `:. n = 9.` |
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