Question

the 8th term of an arithmetic sequence is 12.and it's 12th term 8.what is the algebric expressions for the sequence.? ​

Answer 1

Answer:

$a_{n}$ = 20 - n

Step-by-step explanation:

$a_{n}$ = $a_{1}$ + (n - 1)d

$a_{1}$ + 7d = 12 .... (1)

$a_{1}$ + 11d = 8 ..... (2)

(2) - (1)

11d - 7d = 8 - 12

4d = - 4

d = - 1

$a_{1}$ + 7(- 1) = 12

$a_{1}$ - 7 = 12

$a_{1}$ = 19

$a_{n}$ = 19 - (n - 1) = 19 - n + 1 = 20 - n

$a_{n}$ = 20 - n