Jawabanmu

2014-02-02T13:56:09+07:00
A. S10 = 10/2 (2.50+(10-1) . -4)
S10= 5 (100-36) =320
b. S20 = 20/2 (2. -22+(20-1)4)
S20 = 10(-44+76) = 320
2014-02-02T14:00:00+07:00
Sn=n/2(2a+(n-1)b)
s10=5(100+9.-4)
       =5(100-36)
        =5(64)
         =320
s20=10(2.-22+19.6)
       =10(-44+114)
         =10(70)
         =700