JEE Mains · Maths · STD 11 - 8. sequence and series
If the sum of the first four terms of an A.P. is 6 and the sum of its first six terms is 4, then the sum of its first twelve terms is
- A -20
- B -24
- C -26
- D -22
Answer & Solution
Correct Answer
(D) -22
Step-by-step Solution
Detailed explanation
Sum of first 4 term \(S_4=6\) \(\frac{4}{2}(2 a+3 d)=6 \Rightarrow 2 a+3 d=3\)\(\quad\)....(1) Sum of first 6 terms \(S_6=4\) \(\frac{6}{2}(2 a+5 d)=4 \Rightarrow 2 a+5 d=\frac{4}{3} \ldots . .\)(2) eq. (2) - eq. (1) \((2 a+5 d)-(2 a+3 d)=\frac{4}{3}-3\)…
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