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.
-27, 18 , 9, 0, . . .
A) $a _ { n } = 27 - 9 n ; a _ { 20 } = - 153$
B) $a _ { n } = 36 - 9 n ; a _ { 20 } = - 144$
C) $a _ { n } = 9 n - 27 ; a _ { 20 } = 153$
D) $a _ { n } = 9 n - 36 ; a _ { 20 } = 144$

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.
-27, 18 , 9, 0, . . . 
A) $a _ { n } = 27 - 9 n ; a _ { 20 } = - 153$
B) $a _ { n } = 36 - 9 n ; a _ { 20 } = - 144$
C) $a _ { n } = 9 n - 27 ; a _ { 20 } = 153$
D) $a _ { n } = 9 n - 36 ; a _ { 20 } = 144$

Quizplus · Accepted Answer

The sequence is arithmetic with the first term $a_1 = 27$ and a common difference $d = 18 - 27 = -9$. The formula for the nth term is $a_n = a_1 + (n-1)d = 27 + (n-1)(-9) = 36 - 9n$. For $a_{20}$, substitute $n = 20$: $a_{20} = 36 - 9(20) = -144$.

Write a Formula for the General Term (The Nth Term) an=27−9n;a20=−153a _ { n } = 27 - 9 n ; a _ { 20 } = - 153an​=27−9n;a20​=−153

Write a Formula for the General Term (The Nth Term) $a _ { n } = 27 - 9 n ; a _ { 20 } = - 153$