Answer
A recursive rule for the sequence is $a_1=-20,a_n=a_{n-1}+4$.
Work Step by Step
Use graph to write down the sequence
$-20,-16,-12,-8,...$
The first term is $a_1=-20$.
Calculate difference between each pair of consecutive terms.
$-16-(-20)=-16+20=4$
$-12-(-16)=-12+16=4$
$-8-(-12)=-8+16=4$
The common difference is $d=4$.
So, the sequence is arithmetic.
Recursive equation for an arithmetic sequence.
$a_n=a_{n-1}+d$
Substitute $4$ for $d$.
$a_n=a_{n-1}+4$
Hence, a recursive rule for the sequence is $a_1=-20,a_n=a_{n-1}+4$.
