Write a formula for the general term (the nth term) of the arithmetic sequence. Then use the formula for an to find a20,
the 20th term of the sequence.
-3 , 12 , 21 , 30 , 39 , . . .
A) $a _ { n } = 6 n - 2 ; a _ { 20 } = 118$
B) $a _ { n } = 9 n - 2 ; a _ { 20 } = 178$
C) $a _ { n } = 6 n - 9 ; a _ { 20 } = 111$
D) $a _ { n } = 9 n - 6 ; a _ { 20 } = 174$

Question

Write a formula for the general term (the nth term) of the arithmetic sequence. Then use the formula for an to find a20,
the 20th term of the sequence.
-3 , 12 , 21 , 30 , 39 , . . . 
A) $a _ { n } = 6 n - 2 ; a _ { 20 } = 118$
B) $a _ { n } = 9 n - 2 ; a _ { 20 } = 178$
C) $a _ { n } = 6 n - 9 ; a _ { 20 } = 111$
D) $a _ { n } = 9 n - 6 ; a _ { 20 } = 174$

Quizplus · Accepted Answer

The common difference (d) is 9 (12 - 3 = 9). The first term (a1) is 3. The formula for the nth term of an arithmetic sequence is $a_n = a_1 + (n - 1)d$. Substituting the values, we get $a_n = 3 + (n - 1)9 = 9n - 6$. For the 20th term, $a_{20} = 9(20) - 6 = 180 - 6 = 174$.

Write a Formula for the General Term (The Nth Term) an=6n−2;a20=118a _ { n } = 6 n - 2 ; a _ { 20 } = 118an​=6n−2;a20​=118

Write a Formula for the General Term (The Nth Term) $a _ { n } = 6 n - 2 ; a _ { 20 } = 118$