а(1)=35
а(2)=32
d=a(2)-a(1)
d=-3
a(n)= a(1)+d(n-1)
a(n)=35-3(n-1) <0
35-3n+3<0
-3n<-38
n>38/3
n>12 2/3
n=13
a(13)=a(1)+12d
a(13)=35-36
a(13)=-1
