а3+а6=3;
а2-15-а7;
a1+2d+a1+5d=3;
2a1+7d=3;
a1+d-15=a1+6d;
-5d=-15;
d=3;
2a1+7*3=3;
2a1+21=3;
2a1=-18;
a1=-9;
а3+а6=3;
а2-15-а7;
a1+2d+a1+5d=3;
2a1+7d=3;
a1+d-15=a1+6d;
-5d=-15;
d=3;
2a1+7*3=3;
2a1+21=3;
2a1=-18;
a1=-9;