Jawabanmu

2014-05-09T15:07:37+07:00
30 = 10 +(n-1)8
28 = 8n
 3,5 =n

Sn=  \frac{3,5}{2} ( 2x 10 + (3,5 - 1)8 )
    = 7
1 3 1
2014-05-09T15:10:16+07:00
30= 10 + (n-1) 8
30= 10 + 8n - 8
30= 2 + 8n
8n = 30-2 = 28
n = 28/8 = 3,5

S3,5= 3,5/2 (2 x 10 + (3,5-1) 8)
= 3,5 /2 (40)
= 7
2 2 2