JEE Mains · Maths · STD 11 - 8. sequence and series
Let \(\mathrm{a}_{\mathrm{n}}\) be the \(\mathrm{n}^{\text {th }}\) term of an A. P.
If \(S_n=a_1+a_2+a_3+\ldots+a_n=700, a_6=7\) and \(S_7=7\), then \(\mathrm{a}_{\mathrm{n}}\) is equal to :
- A 56
- B 65
- C 64
- D 70
Answer & Solution
Correct Answer
(C) 64
Step-by-step Solution
Detailed explanation
\(\mathrm{S}_{\mathrm{n}}=700=\frac{\mathrm{n}}{2}[2 \mathrm{a}+(\mathrm{n}-1) \mathrm{d}]\)...(i) \(a_6=7 \Rightarrow a+5 d=7\)...(ii) \(\mathrm{S}_7=7 \Rightarrow \frac{7}{2}(2 \mathrm{a}+6 \mathrm{~d})=7\) \(a+3 d=1\)...(iii) Solve (ii) and (iii)…
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