The first and last term of an $A.P. $ are $a$ and $l$ respectively. If $S$ is the sum of all the terms of the $A.P.$ and the common difference is given by $\frac{\text{l}^2-\text{a}^2}{\text{k}-(\text{l}+\text{a})},$ then $\text{k}=$
- A$S$
- ✓$2S$
- C$3S$
- DNone of these
Answer: B.
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