Question

Find the 18th term of the arithmetic sequence whose common difference is d=-5 and whose first term is (picture)

Answer 1

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:

$a_n=a_1+d(n-1).$

Substituting n=18, a₁=25, and d=-5 in the above equation we get:

$a_{18}=25-5(18-1).$

Simplifying the above result we get:

$\begin{gathered} a_{18}=25-5(17)=25-85 \\ =-60. \end{gathered}$

Answer:

$a_{18}=-60.$