Jawabanmu

2014-02-20T16:50:12+07:00
U5=a+b(n-1)
37=a+14(4)
37=a+56
-19=a=U1

U9=-19+14(8)
U9=-19+112
U9=93

S9=(U1+Un)n : 2
    =(-19+93)9 : 2
    =74 x 4.5
S9=333