Jawabanmu

2014-04-14T20:21:28+07:00
U7 = a+6b = 20
Un = 44
S3 = 3/2 (U1+Un) = 15
       3/2 ( U1+44) = 15
U1+44 = 10
U1 = 10-44
U1 = -34

suku tengah = 1/2 (U1+Un)
1/2 ( -34 + 44)
1/2 ( 10) = 5