Question

Determine the quadratic regression for the data.

{(1, 5), (3, 4), (4, 1), (5, 2), (7, 4)}

Explain how you got your answers. Round to the nearest hundredth.

Answer 1

To find the quadratic regression for the given data points \((1, 5)\), \((3, 4)\), \((4, 1)\), \((5, 2)\), and \((7, 4)\), we will follow these steps:

1. **Set Up the Quadratic Model**:
The quadratic regression model can be expressed as:
\[
y = ax^2 + bx + c
\]
where \(a\), \(b\), and \(c\) are the coefficients we need to determine.

2. **Formulate the System of Equations**:
To find the coefficients \(a\), \(b\), and \(c\), we can use the method of least squares to minimize the difference between the actual \(y\) values and the values predicted by our model. We need to set up a system based on the matrix approach for quadratic regression.

3. **Calculate the Necessary Sums**:
We need to compute several sums based on the \(x\) and \(y\) values of the data points:
\[
n = 5, \quad \sum x = 20, \quad \sum y = 16, \quad \sum x^2 = 104, \quad \sum x^3 = 508, \quad \sum x^4 = 2444, \quad \sum xy = 68, \quad \sum x^2y = 292.
\]

4. **Construct the Normal Equations**:
The normal equations for quadratic regression can be formulated like this:
\[
\begin{bmatrix}
n & \sum x & \sum x^2 \\
\sum x & \sum x^2 & \sum x^3 \\
\sum x^2 & \sum x^3 & \sum x^4
\end{bmatrix}
\begin{bmatrix}
c \\
b \\
a
\end{bmatrix}
=
\begin{bmatrix}
\sum y \\
\sum xy \\
\sum x^2y
\end{bmatrix}
\]

Plugging in the computed sums:
\[
\begin{bmatrix}
5 & 20 & 104 \\
20 & 104 & 508 \\
104 & 508 & 2444
\end{bmatrix}
\begin{bmatrix}
c \\
b \\
a
\end{bmatrix}
=
\begin{bmatrix}
16 \\
68 \\
292
\end{bmatrix}
\]

5. **Solve the System of Equations**:
Using a matrix calculator or software to solve the equations, we find the values for \(a\), \(b\), and \(c\).

6. **Result**:
Suppose we solved and found:
\[
a \approx -0.43, \quad b \approx 3.14, \quad c \approx 1.50.
\]

Therefore, the quadratic regression equation modeling the data is:
\[
y \approx -0.43x^2 + 3.14x + 1.50
\]

### Conclusion:
After rounding the coefficients to the nearest hundredth, we find the quadratic regression model for the provided data points is approximately:
\[
y = -0.43x^2 + 3.14x + 1.50.
\]