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The number of hours of daylight on the summer solstice (the 172nd day of the year) is 15.3, and the number of hours of daylight on the winter solstice (the 355th day of the year) is 9.1. Complete the function below to model this data. The period is 365 days.

[tex]\[ y = 3.1 \cos \left(\frac{2 \pi}{365}(x - 172) + [?] \right) \][/tex]


Sagot :

Sure, let's go through the process of modeling the hours of daylight with the information provided.

Given data:
- The number of hours of daylight on the summer solstice: [tex]\( y_{\text{summer solstice}} = 15.3 \)[/tex]
- The number of hours of daylight on the winter solstice: [tex]\( y_{\text{winter solstice}} = 9.1 \)[/tex]
- The period of the cycle: [tex]\( T = 365 \)[/tex] days
- The day of the year for the summer solstice: [tex]\( x_{\text{summer solstice}} = 172 \)[/tex]
- The day of the year for the winter solstice: [tex]\( x_{\text{winter solstice}} = 355 \)[/tex]

To create a function [tex]\( y = a \cos\left( \omega (x - \phi) \right) + D \)[/tex] that models the daylight hours, we need to determine:
1. The vertical shift ([tex]\( D \)[/tex]).
2. The amplitude ([tex]\( A \)[/tex]).
3. The angular frequency ([tex]\( \omega \)[/tex]).
4. The phase shift ([tex]\( \phi \)[/tex]).

Step-by-step solution:

1. Vertical Shift ([tex]\( D \)[/tex]):
The vertical shift is the average of the maximum and minimum values of the function.
[tex]\[ D = \frac{y_{\text{summer solstice}} + y_{\text{winter solstice}}}{2} \][/tex]
Given the values:
[tex]\[ D = \frac{15.3 + 9.1}{2} = 12.2 \][/tex]

2. Amplitude ([tex]\( A \)[/tex]):
The amplitude is half the difference between the maximum and minimum values of the function.
[tex]\[ A = \frac{y_{\text{summer solstice}} - y_{\text{winter solstice}}}{2} \][/tex]
Given the values:
[tex]\[ A = \frac{15.3 - 9.1}{2} = 3.1 \][/tex]

3. Angular Frequency ([tex]\( \omega \)[/tex]):
The angular frequency is related to the period of the function.
[tex]\[ \omega = \frac{2\pi}{T} \][/tex]
Given the period [tex]\( T = 365 \)[/tex] days:
[tex]\[ \omega = \frac{2\pi}{365} \approx 0.017214 \][/tex]

4. Phase Shift ([tex]\( \phi \)[/tex]):
The maximum value occurs at [tex]\( x = 172 \)[/tex] (the summer solstice). In a cosine function, this corresponds to [tex]\( \cos(0) = 1 \)[/tex], so we need to solve for [tex]\( \phi \)[/tex] when [tex]\( x = 172 \)[/tex].
[tex]\[ \omega (x_{\text{summer solstice}} - \phi) = 0 \][/tex]
Therefore:
[tex]\[ 0.017214 \times (172 - \phi) = 0 \][/tex]
Hence:
[tex]\[ \phi = 172 \][/tex]

Putting it all together, our function [tex]\( y = A \cos(\omega (x - \phi)) + D \)[/tex] becomes:
[tex]\[ y = 3.1 \cos \left( \frac{2\pi}{365} (x - 172) \right) + 12.2 \][/tex]