a_(1)+(a_(1)+d)+(a_(1)+2d)+(a_(1)+3d)+(a_(1)+4d)+(a_(1)+5d)=264 ⇒[b] 6a_(1)+15d=264[/b]
а_(5)+а_(6)=5a_(1)
a_(1)+4d+a_(1)+5d=5a_(1) ⇒ 3a_(1)=9d
a_(1)=3d
[b] 6a_(1)+15d=264[/b]
6*3d+15d=264
33d=264
d=8
a_(1)=3d=3*8=24
а_(2)=а_(1)+d=24+8=32
a_(3)=a_(2)+d=32+8=40
a_(4)=a_(3)+d=40+8=48
a_(5)=a_(4)+d=48+8=56
a_(6)=a_(5)+d=56+8=64