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Can you write a function rule that matches this table of values?

\begin{tabular}{|c|c|c|c|c|}
\hline
[tex]$x$[/tex] & 3 & 5 & 7 & 9 \\
\hline
[tex]$y$[/tex] & 13 & 31 & 57 & 91 \\
\hline
\end{tabular}

Sagot :

Absolutely! To find a function rule that matches the given table of values, we start by noting the pairs of \((x, y)\) values:

[tex]\[ \begin{align*} (3, 13), \\ (5, 31), \\ (7, 57), \\ (9, 91). \end{align*} \][/tex]

We aim to find a polynomial function of the form:

[tex]\[ y = ax^2 + bx + c \][/tex]

We will determine the coefficients \(a\), \(b\), and \(c\).

### Step-by-Step Solution

1. Set up a system of equations:
For each pair \((x, y)\), substitute the values into the polynomial equation:
[tex]\[ \begin{align*} 13 &= a(3)^2 + b(3) + c, \\ 31 &= a(5)^2 + b(5) + c, \\ 57 &= a(7)^2 + b(7) + c, \\ 91 &= a(9)^2 + b(9) + c. \end{align*} \][/tex]

2. Expand and simplify:
[tex]\[ \begin{align*} 13 &= 9a + 3b + c, \\ 31 &= 25a + 5b + c, \\ 57 &= 49a + 7b + c, \\ 91 &= 81a + 9b + c. \end{align*} \][/tex]

3. Solve the system of equations:
Solving the above system, we find:
[tex]\[ a = 1, \quad b = 1, \quad c = 1 \][/tex]

### Final Function Rule

From the coefficients obtained, the polynomial function that matches the given table of values is:

[tex]\[ y = x^2 + x + 1 \][/tex]

### Verification

Let's verify by substituting each value of \(x\) back into the function:

1. For \(x = 3\):
[tex]\[ y = 3^2 + 3 + 1 = 9 + 3 + 1 = 13 \][/tex]
2. For \(x = 5\):
[tex]\[ y = 5^2 + 5 + 1 = 25 + 5 + 1 = 31 \][/tex]
3. For \(x = 7\):
[tex]\[ y = 7^2 + 7 + 1 = 49 + 7 + 1 = 57 \][/tex]
4. For \(x = 9\):
[tex]\[ y = 9^2 + 9 + 1 = 81 + 9 + 1 = 91 \][/tex]

Therefore, the function rule [tex]\(y = x^2 + x + 1\)[/tex] correctly matches the given table of values.