a)
a_(10)=a_(1)+9d=-24+9*5=[b]21[/b]
б)
a_(5)=a_(1)+4d
a_(3)=a_(1)+2d
a_(5)-a_(3)=2d
2d=(9,2-4)
d=[b]2,6[/b]
в)
a_(7)=a_(1)+6d
-10=14+6d
6d=-10-14
6d=-24
d=-4
S_(10)=(2a_(1)+9d)/2=(2*14+9*(-4))/2=[b]-4[/b]
2
a_(1)=6
a_(11)=66
S_(11)=(6+66)*11/2=[b]396[/b]
1.
a)
a_(9)=a_(1)+8d=8+8*(-3)[b]=-16[/b]
б)
a_(8)=a_(1)+7d
a_(6)=a_(1)+5d
a_(8)-a_(6)=2d
d=(0,6-8)/2=[b]-3,7[/b]
d)
a_(10)=a_(1)+9d
42=-12+9d
9d=54
d=6
S_(7)=(2a_(1)+6d)*7/2=(2*(-12)+6*6)*7/2=[b]42[/b]
2.
a_(1)=4
a_(16)=64
S_(16)=(4+64)*16/2=544