Answer:
Part a)
[tex]m \to \: a(m) \\ 1 \to \: 100 \\ 2 \to \: 140 \\ 3 \to \: 180 \\ 3\to \: 220 \\ 4 \to \: 260[/tex]
Part b)
[tex]a_n=a_{n-1}+40 \\ a_1=100[/tex]
Step-by-step explanation:
Part a)
Erina already $100 saved.
This means
[tex]a_1=100[/tex]
She plans on saving 40 dollars a month.
This means that the common difference is
[tex]d = 40[/tex]
[tex]m \to \: a(m) \\ 1 \to \: 100 \\ 2 \to \: 140 \\ 3 \to \: 180 \\ 3\to \: 220 \\ 4 \to \: 260[/tex]
Part b)
The recursive formula for an arithmetic sequence is given as
[tex]a_n=a_{n-1}+d[/tex]
The common difference is d=40 and the first term is
[tex]a_1=100[/tex]
We substitute d=40 into the formula to get:
[tex]a_n=a_{n-1}+40 \\ a_1=100[/tex]