1. **State the problem:**
We have an account with an initial investment of $1 that pays 150% interest per month but also charges a fixed fee of 3 per month. We want to find the value of the account $y$ after $x$ months for $x = -2, -1, 0, 1, 2$.
2. **Write the formula:**
The account grows by 150% per month, meaning it multiplies by $1 + 1.5 = 2.5$ each month, but we subtract 3 each month as a fee.
The recursive formula is:
$$y_{x} = 2.5 y_{x-1} - 3$$
with initial value $y_0 = 1$.
3. **Calculate values step-by-step:**
- For $x=0$, $y_0 = 1$ (given).
- For $x=1$:
$$y_1 = 2.5 \times y_0 - 3 = 2.5 \times 1 - 3 = 2.5 - 3 = -0.5$$
- For $x=2$:
$$y_2 = 2.5 \times y_1 - 3 = 2.5 \times (-0.5) - 3 = -1.25 - 3 = -4.25$$
4. **Calculate for negative $x$ (going backwards):**
We solve for $y_{x-1}$:
$$y_x = 2.5 y_{x-1} - 3 \implies y_{x-1} = \frac{y_x + 3}{2.5}$$
- For $x=0$, $y_0=1$ (given).
- For $x=-1$:
$$y_{-1} = \frac{y_0 + 3}{2.5} = \frac{1 + 3}{2.5} = \frac{4}{2.5} = 1.6$$
- For $x=-2$:
$$y_{-2} = \frac{y_{-1} + 3}{2.5} = \frac{1.6 + 3}{2.5} = \frac{4.6}{2.5} = 1.84$$
5. **Complete the table:**
| x | y |
|----|------|
| -2 | 1.84 |
| -1 | 1.6 |
| 0 | 1 |
| 1 | -0.5 |
| 2 | -4.25|
6. **Type of function:**
Because the account value decreases after $x=0$ and becomes negative, this is not a pure exponential growth or decay. The fixed fee causes the value to decrease despite the growth factor. So it is neither pure growth nor decay exponential.
7. **Asymptote:**
Find steady state $y$ where $y = 2.5 y - 3$:
$$y = 2.5 y - 3 \implies 3 = 2.5 y - y = 1.5 y \implies y = \frac{3}{1.5} = 2$$
So the horizontal asymptote is $y=2$.
8. **Y-intercept:**
At $x=0$, $y=1$.
9. **Graph description:**
The graph crosses $y=1$ at $x=0$, rises to about 1.6 and 1.84 for negative $x$, and then falls below zero for positive $x$. The horizontal asymptote is $y=2$.
Account Growth 3D403F
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