Jawabanmu

2014-09-11T13:52:46+07:00
Dik: a= 1
b= U2-U1 = U3 - U2= 1
dit: Sn=?
peny:
Un= a+ (n-1) x b
28= 1 + (n-1) x 1
28 = 1 + n-1
n= 28

Sn= (n : 2) x (a+Un)
= (28 : 2) x (1 + 28)
= 14 x 29
= 406