1
a1=(1-1)/2=0
a2=(4-2)/2=1
a3=(9-3)/2=3
2
a10=a1+9d
a10=2-3*9=2-27=-25
S10=(a1+a10)*n/2
S10=(2-25)*10/2=-23*5=-115
3
b6=b1*q^5
b6=4*1/32=1/8
S6=b1(1-q^6)/(1-q)
S6=1*(1-164)/(1-1/2)=4*63/64:1/2=(4*63*2)/64=63/8=7,875
4
a1=1 a2=1/3 a3=1/9
a2/a1=1/3:1=1/3
a3:a2=1/9:1/3=1/9*3/1=1/3
a2/a1=a3/a2=q-знаменатель прогрессии
s5=b1(1-q^5)/(1-q)
S5=1*(1-1/243)/(1-1/3)=242/243:2/3=242/243*3/2=121/81=1 40/81