Write a formula for the general term (the nth term) of the arithmetic sequence. Then use the formula for $$\mathbf { a } _ { \mathbf { n } }$$ to find $$a _ { 20 }$$ , the 20th term of the sequence.
-$1,5,9,13,17 , \ldots$
A) $a _ { n } = 4 n - 3 ; a _ { 20 } = 77$
B) $a _ { n } = 3 n - 4 ; a _ { 20 } = 56$
C) $a _ { n } = 4 n + 3 ; a _ { 20 } = 83$
D) $a _ { n } = n + 4 ; a _ { 20 } = 24$

Question

Quizplus · Accepted Answer

The common difference in the sequence is 4, and the first term is 1. The formula for the nth term of an arithmetic sequence is $a_n = a_1 + (n - 1)d$, where $a_1$ is the first term and $d$ is the common difference. Substituting $a_1 = 1$ and $d = 4$ gives $a_n = 1 + (n - 1)4 = 4n - 3$. For $n = 20$, $a_{20} = 4(20) - 3 = 80 - 3 = 77$.

Write a Formula for the General Term (The Nth Term) an\mathbf { a } _ { \mathbf { n } }an​

Write a Formula for the General Term (The Nth Term) $\mathbf { a } _ { \mathbf { n } }$