3
a5=3;a8=11
d=(a8-a5)/3=(11-3)/3=8/3
a1=a5-4d=3-32/3=-23/3
a7=a8-d=11-8/3=25/3
a4=a5-d=3-8/3=1/3
S6=(2a1+5d)*6/2=(-46/3+40/3)*3=-2*3=-6
4
a3=0,027;a5=0,003
d=(a5-a3)/2=-0,012
5
S11=-147;a1=0,2
S11=(2a1+10d)*11/2
(0,4+10d)*11=-294
0,4+10d=-294/11
10d=-294/11-2/5=(-1470-22)/55
d=-1492/550
d=-2 196/275