а10=а1+9d а1=а10-9d
а11=а1+10а a1=a11-10d
a10-9d=a11-10d
5-9d=-4-10d
10d-9d=-4-5
d= -9
a1= 5 - 9×(-9)=5+45=50
a5=a1+4d= 50 + 4 ×(-9)= 50-36=14
a21=a1+20d=50+20×(-9)=50-180=-130
а10=а1+9d а1=а10-9d
а11=а1+10а a1=a11-10d
a10-9d=a11-10d
5-9d=-4-10d
10d-9d=-4-5
d= -9
a1= 5 - 9×(-9)=5+45=50
a5=a1+4d= 50 + 4 ×(-9)= 50-36=14
a21=a1+20d=50+20×(-9)=50-180=-130