#### Answer

Linear function for $a_{n}$ = -4 n + 5

#### Work Step by Step

From graph,
If n = 1 then $a_{n}$ = 1, write this information as point form (n, $a_{n}$) = (1, 1)
If n = 2 then $a_{n}$ = -3, write this information as point form (n, $a_{n}$) = (2, -3)
Slop of the line join both points (1, 1) and (2, -3) = $\frac{-3-1}{2-1}$ = -4
Equation for straight line which join both the points.
$a_{n}$ = -4n + x
where x = constant find by put $a_{n}$ = 1 if n = 1.
1 = -4 + x
x = 5
then
$a_{n}$ = -4 n + 5
Linear function for $a_{n}$ = -4 n + 5