Answer:
a1 = 17
an+1 = an +0.5
Explanation:
Let
n ----> the number of months
A ---> the length of Janina's hair
we know that
The linear equation in slope intercept form is equal to
![A=mn+a_1](https://img.qammunity.org/2021/formulas/mathematics/middle-school/kpngmlowsperrcni5fut1m88l7jallpdbd.png)
where
m is the slope or unit rate
a_1 is the initial value or y-intercept
In this problem we have
![m=0.5\ in/month](https://img.qammunity.org/2021/formulas/mathematics/middle-school/wz9tvc379epnoh0iv3zs4qj8aprbah1thb.png)
![a_1=17\ in](https://img.qammunity.org/2021/formulas/mathematics/middle-school/qsgox09td3ya3ddu6wl4e4dzkenssmr9h9.png)
substitute
![A=0.5n+17](https://img.qammunity.org/2021/formulas/mathematics/middle-school/aandpu8suiukmd12aggxu4d6lenwfwi2bl.png)
This equation can be expressed as
![a_n_+_1=a_n+0.5n](https://img.qammunity.org/2021/formulas/mathematics/middle-school/xvw6uq9cu677ngw2ashvjki1l4cqfbg8w2.png)
where
![a_1=17](https://img.qammunity.org/2021/formulas/mathematics/middle-school/n8zgfh8ms6ql58zrtxoc0ye7qkkeopy6pa.png)