find S1 abd S2.
S1 = U1 i.e. first term.
S2 - S1 = U2.
U2 - U1 = d i.e. the common difference.
Now proceed.
The sum of the first n terms of a certain progression is given by Sn= n^2 +3n
Find an expression for Sn-1 and deduce an expression for Un
I managed to figure out Un is 2n+2 but i cant quite get my head around the Sn-1 any help on this would be greatly appreciated
Hello, pmh118!
. .
. . . . no
(a) To find , replace with .
. . .
. . .
(b) The common difference is the difference of two consecutive terms.
. . .
. . . .[1]
. . . Sum of the first terms: .
. . .
. . . Substitute [1]: .
. . . Solve for .[2]
. . . The term is: .
. . . Substitute [1] and [2]: .
. . . . . . . . . . . . . . . . . . . .