The explicit formula of an arithmetic sequence:
[tex]a_n=a_1+(n-1)d[/tex]
We have:
[tex]a_1=-100,\ a_2=-70,\ a_3=-40;\ a_4=-10,\ ...\\\\d=a_{n+1}-a_n\to d=-70-(-100)=-70+100=30[/tex]
Substitute:
[tex]a_n=-100+(n-1)(30)=-100+30n-30=30n-130[/tex]
Answer: an = 30n - 130
