Question

Help please.....
The third term of an arithmetic sequence is 21, and the eighth term is 56. The first term is _____.

Answer 1

use the general formula of n'th term, TWICE
\(\Large a_n = a_1 +(n-1)d\)

a1 = 1st term
d is the common difference

Answer 2

hey um im not sure how to solve for that :o

Answer 3

ok,
1st equation,
3rd term is 21
so,
n =3
a3 = 21

\(\large 21 = a_1 + (3-1)d \\ 21 = a_1 +2 d \)

can you find the 2nd equation, similarly ?

Answer 4

is a1 7 ?

Answer 5

yes!
that correct :)

Answer 6

yay thank you :D

Answer 7

welcome ^_^