S27=(2a1+26d)*27/2=60
S5=(2a1+4d)*5/2=27
(2a1+26d)*27=120
(2a1+4d)*5=54
2a1+26d=120/27
2a1+4d=54/5
1уравн отнимаем 2е ур
26d-4d=120/27 - 54/5
22d=600/135 - 1458/135
22d=-858/135
d=-858/135÷22
d=-858/135*1/22
d=-39/135
d=-13/45
2*a1 +4*(-13/45)=54/5
2a1-52/45=54/5
2a1=54/5 +52/45
2a1=486/45 + 52/45
2a1=538/45
a1=538/45 :2
a1=538/45 :1/2
a1=269/45
a1=5цел 44/45
