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How many terms of the series 2 + 6 + 18 + …. Must be taken to make the sum equal to 728? |
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Answer» Given: Sum of GP = 728 ∴ Common Ratio = r = \(\frac{6}{2}\) = 3 a = 2 To find: Number of terms = n. Sum of GP for n terms = \(\frac{a(r^n-1)}{r-1}\) ⇒ 728 = \(\cfrac{2(3^n -1)}{3-1}\) ⇒ 728 = 3n - 1 ⇒ 729 = 3n ⇒ 36 = 3n ∴ n = 6. |
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