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Find the cubic function that models the data in the table below.

\begin{tabular}{|c|c|c|c|c|c|c|c|}
\hline [tex]$x$[/tex] & -2 & -1 & 0 & 1 & 2 & 3 & 4 \\
\hline [tex]$y$[/tex] & -20 & -4 & 0 & -2 & -4 & 0 & 16 \\
\hline
\end{tabular}

[tex]\[ y = x^3 - 3x^2 \][/tex]

(Simplify your answer. Do not factor. Use integers or decimals for any numbers in the expression. Round to three decimal places as needed.)


Sagot :

### Solution:

To find a cubic function that models the given data, we need to determine the cubic polynomial [tex]\(y = ax^3 + bx^2 + cx + d\)[/tex] that fits the data points [tex]\((x, y)\)[/tex].

Here, the given data points are:

[tex]\[ \begin{aligned} x: & \quad -2, -1, 0, 1, 2, 3, 4, \\ y: & \quad -20, -4, 0, -2, -4, 0, 16. \end{aligned} \][/tex]

We will define the function in the form:
[tex]\[ y = ax^3 + bx^2 + cx + d. \][/tex]

Using a method of polynomial fitting (e.g., least squares fit), we can find the coefficients [tex]\(a\)[/tex], [tex]\(b\)[/tex], [tex]\(c\)[/tex], and [tex]\(d\)[/tex]. The best-fit cubic polynomial through these points is:

[tex]\[ y = 1.000x^3 - 3.000x^2 + 0x + 0 \][/tex]

This gives us the function:
[tex]\[ y = x^3 - 3x^2 \][/tex]

### Evaluation of the Function:

Let's check the values by plugging in the given [tex]\(x\)[/tex]-values:

1. For [tex]\(x = -2\)[/tex]:
[tex]\[ y = (-2)^3 - 3(-2)^2 = -8 - 12 = -20 \][/tex]

2. For [tex]\(x = -1\)[/tex]:
[tex]\[ y = (-1)^3 - 3(-1)^2 = -1 - 3 = -4 \][/tex]

3. For [tex]\(x = 0\)[/tex]:
[tex]\[ y = (0)^3 - 3(0)^2 = 0 \][/tex]

4. For [tex]\(x = 1\)[/tex]:
[tex]\[ y = (1)^3 - 3(1)^2 = 1 - 3 = -2 \][/tex]

5. For [tex]\(x = 2\)[/tex]:
[tex]\[ y = (2)^3 - 3(2)^2 = 8 - 12 = -4 \][/tex]

6. For [tex]\(x = 3\)[/tex]:
[tex]\[ y = (3)^3 - 3(3)^2 = 27 - 27 = 0 \][/tex]

7. For [tex]\(x = 4\)[/tex]:
[tex]\[ y = (4)^3 - 3(4)^2 = 64 - 48 = 16 \][/tex]

The function [tex]\( y = x^3 - 3x^2 \)[/tex] matches all the given [tex]\( (x, y) \)[/tex] pairs perfectly.

### Final Simplified Answer:

So, the cubic function that models the provided data is:
[tex]\[ y = x^3 - 3x^2 \][/tex]

No further simplification is needed, as this equation is already in its most simplified form.