Jawaban :
U1+U2+U3+....+U10=S10=-110....U11+U12=2....a+10b+a+11b=2....2a+21b=2 (I)....S10=10/2 (2a+(10-1)b)...-110=5 (2a+9b)....-22=2a+9b(II)....kita eliminasi persamaan I dan II .... 12b=24...b=2....
2a+21 (2)=2...2a+42=2...a=-20...U1+U2=a+a+b=-20-20+2=-38