Jawabanmu

2014-03-25T19:56:23+07:00
U7 = 29
U3 = 13 _
4 b = 16
   b = 16:4 = 4
a = 5

Sn = n/2. (2a+(n-1)b)
S25 = 25/2 (2.5+( 25 -1 ) 4)
       = 12,5 . (10+24.4)
       = 12,5 . (10+ 96)
       = 12,5. 106
       = 1325