Help with arithmetic sequence

Sep 2016
1
0
Irvine California
In an arithmetic sequence, the seventh term is 3 and the sixteenth term is 9. use arithmetic means to determine the common difference and the first term of the sequence

Thanks for the help!
 

romsek

MHF Helper
Nov 2013
6,738
3,034
California
$a_k = a_1+(k-1) d$

$a_7 = a_1 + 6d = 3$

$a_{16}=a_1 + 15d = 9$

not sure about using arithmetic means but subtracting one equation from the other gets you

$9d = 6$

$d = \dfrac 2 3$

$a_1 = -1$
 
Feb 2015
2,255
510
Ottawa Ontario
Did you google "arithmetic sequences"?