JEE Mains · Maths · STD 11 - 8. sequence and series
In an increasing geometric progression ol positive terms, the sum of the second and sixth terms is \(\frac{70}{3}\) and the product of the third and fifth terms is \(49\). Then the sum of the \(4^{\text {th }}, 6^{\text {th }}\) and \(8^{\text {th }}\) terms is :-
- A \(96\)
- B \(78\)
- C \(91\)
- D \(84\)
Answer & Solution
Correct Answer
(B) \(78\)
Step-by-step Solution
Detailed explanation
\( \mathrm{T}_2+\mathrm{T}_6=\frac{70}{3} \) \( \mathrm{ar}+\mathrm{ar}^5=\frac{70}{3} \) \( \mathrm{~T}_3 \cdot \mathrm{T}_5=49 \) \( \mathrm{ar}^2 \cdot \mathrm{ar}^4=49 \) \( \mathrm{a}^2 \mathrm{r}^6=49 \) \( \mathrm{ar}^3=+7, \mathrm{a}=\frac{7}{\mathrm{r}^3} \)…
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