Jawabanmu

2014-03-21T23:01:39+07:00
A=2...U12-U7=a+11b-(a+6b)=5b=30....b=6....Sn=n/2 (2a+(n-1) b)=50/2 (2*2+49*6)=29400
2014-03-21T23:10:08+07:00
A = 2
U12 - U7 = 30
b =  \frac{U12-U7}{12-7} =  \frac{30}{5} = 6
Sn =  \frac{n}{2} (2a+(n-1)b)
S50 = 25 ( 4 + (49)6)
S50 = 25 ( 4+294)
S50 = 7450

semoga membantu :)