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 l2−a2k−(l+a)l2−a2k−(l+a) then k = ?

• ক 3S
• খ S
• গ 2S ✅ সঠিক উত্তর
• ঘ S^2