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The table shows the wavelength of the sound produced by keys on a piano [tex]\( x \)[/tex] keys away from the A above middle C.

[tex]\[
\begin{tabular}{|c|c|}
\hline
\begin{tabular}{c}
Number of keys above the \\
A above middle C
\end{tabular} & \begin{tabular}{c}
Wavelength \\
$( \text{cm} )$
\end{tabular} \\
\hline
0 & 78.41 \\
\hline
2 & 69.85 \\
\hline
3 & 65.93 \\
\hline
6 & 55.44 \\
\hline
10 & 44.01 \\
\hline
\end{tabular}
\][/tex]

Using the exponential regression model, which is the best prediction of the wavelength of the key that is 8 above the A above middle C?

A. 49.31 cm
B. 49.44 cm
C. 49.73 cm
D. 49.78 cm


Sagot :

To find the best prediction of the wavelength of the key that is 8 keys above the A above middle C, let's follow these steps:

1. Data Summary and Preparation: We have the following data points:

[tex]\[ \begin{array}{|c|c|} \hline \text{Number of keys}, x & \text{Wavelength} (\text{cm}), y \\ \hline 0 & 78.41 \\ \hline 2 & 69.85 \\ \hline 3 & 65.93 \\ \hline 6 & 55.44 \\ \hline 10 & 44.01 \\ \hline \end{array} \][/tex]

2. Logarithmic Transformation: When performing exponential regression, convert the dependent variable [tex]\( y \)[/tex] (wavelength) using the natural logarithm [tex]\( \ln(y) \)[/tex].

3. Linear Regression on the Transformed Data: Perform a linear regression on the data [tex]\((x, \ln(y))\)[/tex] to find the linear relationship:

[tex]\[ \text{ln}(y) = \text{slope} \cdot x + \text{intercept} \][/tex]

From the regression analysis, we have:
- Slope: [tex]\( -0.05775194578546561 \)[/tex]
- Intercept: [tex]\( 4.3618808452540865 \)[/tex]

4. Make Prediction for [tex]\( x = 8 \)[/tex]:

Substitute [tex]\( x = 8 \)[/tex] into the linear regression equation to find the predicted [tex]\(\text{ln}(y)\)[/tex]:

[tex]\[ \text{ln}(y)_{\text{pred}} = (-0.05775194578546561) \times 8 + 4.3618808452540865 \][/tex]

This simplifies to:

[tex]\[ \text{ln}(y)_{\text{pred}} = 3.8998652789703616 \][/tex]

5. Convert Back to Original Scale: Convert the [tex]\(\text{ln}(y)\)[/tex] value back to [tex]\( y \)[/tex] by exponentiating it:

[tex]\[ y_{\text{pred}} = e^{3.8998652789703616} \][/tex]

This yields the predicted wavelength:

[tex]\[ y_{\text{pred}} = 49.39579400502108 \, \text{cm} \][/tex]

6. Choose the Closest Answer:

Looking at the possible choices:
- 49.31 cm
- 49.44 cm
- 49.73 cm
- 49.78 cm

The best prediction of the wavelength of the key that is 8 keys above the A above middle C is:

[tex]\[ \boxed{49.44 \, \text{cm}} \][/tex]

This value is the closest to the calculated predicted wavelength of approximately 49.39579400502108 cm.
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