If Sn dwnotes the sum of an AP whose common difference is d and first term is a find Sn-2,Sn-1,Sn-2

If Sn dwnotes the sum of an AP whose common difference is d and first

1.	If Sn dwnotes the sum of an AP whose common difference is d and first term is a find Sn-2,Sn-1,Sn-2
Answer» Refer the example in RS AGARWAL BOOK