Answer:
![f(x) = 7x + 30](https://tex.z-dn.net/?f=f%28x%29%20%3D%207x%20%2B%2030)
Step-by-step explanation:
We need at least two points to write the equation of a straight line.
The recursive formula that Elijah wrote is:
![f(0) = 30](https://tex.z-dn.net/?f=f%280%29%20%3D%2030)
![f(n + 1) = f(n) + 7](https://tex.z-dn.net/?f=f%28n%20%2B%201%29%20%3D%20f%28n%29%20%2B%207)
When we substitute n=0, we get:
![f(0 + 1) = f(0) + 7](https://tex.z-dn.net/?f=f%280%20%2B%201%29%20%3D%20f%280%29%20%2B%207)
![f(1) = 30 + 7](https://tex.z-dn.net/?f=f%281%29%20%3D%2030%20%2B%207)
![f(1) = 37](https://tex.z-dn.net/?f=f%281%29%20%3D%2037)
The points (0,30) and (1,37) lies on this line.
The equation of this line is of the form:
![f(x) = mx + b](https://tex.z-dn.net/?f=f%28x%29%20%3D%20mx%20%2B%20b)
where b =30 is the y-intercept and m=7 is the slope.
We plug in these values to get:
![f(x) = 7x + 30](https://tex.z-dn.net/?f=f%28x%29%20%3D%207x%20%2B%2030)
Note that the slope of the line is equal to the common difference of the Arithmetic Sequence.
You could also use the two points to find the slope:
![m = \frac{37 - 30}{1 - 0} = 7](https://tex.z-dn.net/?f=m%20%3D%20%20%5Cfrac%7B37%20-%2030%7D%7B1%20-%200%7D%20%20%3D%207)