To answer this question we will use the following formula to compute the nth term of an arithmetic sequence with a common difference of d and first term a₁:
[tex]a_n=a_1+d(n-1).[/tex]
Substituting n=18, a₁=25, and d=-5 in the above equation we get:
[tex]a_{18}=25-5(18-1).[/tex]
Simplifying the above result we get:
[tex]\begin{gathered} a_{18}=25-5(17)=25-85 \\ =-60. \end{gathered}[/tex]
Answer:
[tex]a_{18}=-60.[/tex]
