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Practice Assignment 2.6: Transformations of Sine and Cosine II

Question 5

Find a possible formula for the trigonometric function whose values are in the following table.

[tex]\[
\begin{tabular}{|r|r|r|r|r|r|r|r|}
\hline
x & 0 & 3 & 6 & 9 & 12 & 15 & 18 \\
\hline
y & 2 & -3 & 2 & 7 & 2 & -3 & 2 \\
\hline
\end{tabular}
\][/tex]

Hint: Plot the points and sketch your own graph if needed.

[tex]\[
y = \square
\][/tex]

Sagot :

To find a possible formula for the trigonometric function given the values in the table, we will analyze the characteristics of the function step by step.

The table is as follows:

[tex]\[ \begin{array}{|r|r|r|r|r|r|r|r|} \hline x & 0 & 3 & 6 & 9 & 12 & 15 & 18 \\ \hline y & 2 & -3 & 2 & 7 & 2 & -3 & 2 \\ \hline \end{array} \][/tex]

1. Determine the Period:
By observing the pattern of the values, we can notice that the function repeats its values every 12 units along the x-axis. Therefore, the period of the function is [tex]\(12\)[/tex].

2. Determine the Amplitude:
The amplitude of a trigonometric function is half the difference between the maximum and minimum values of [tex]\(y\)[/tex].

Maximum [tex]\(y\)[/tex] value: [tex]\(7\)[/tex] (at [tex]\(x = 9\)[/tex])
Minimum [tex]\(y\)[/tex] value: [tex]\(-3\)[/tex] (at [tex]\(x = 3\)[/tex] and [tex]\(x = 15\)[/tex])

Amplitude [tex]\(A\)[/tex] is calculated as follows:
[tex]\[ A = \frac{\text{max}_y - \text{min}_y}{2} = \frac{7 - (-3)}{2} = \frac{10}{2} = 5 \][/tex]

3. Determine the Vertical Shift (Midline):
The vertical shift, or the midline of the function, is the average of the maximum and minimum [tex]\(y\)[/tex] values.

Vertical shift [tex]\(D\)[/tex] is calculated as follows:
[tex]\[ D = \frac{\text{max}_y + \text{min}_y}{2} = \frac{7 + (-3)}{2} = \frac{4}{2} = 2 \][/tex]

4. Determine the Frequency:
The frequency [tex]\(B\)[/tex] relates to the period [tex]\(T\)[/tex] via the formula:
[tex]\[ B = \frac{2\pi}{T} \][/tex]
Given that the period [tex]\(T\)[/tex] is [tex]\(12\)[/tex]:
[tex]\[ B = \frac{2\pi}{12} = \frac{\pi}{6} \approx 0.5236 \][/tex]

5. Determine the Phase Shift:
The phase shift will depend on the specific form of the trigonometric function we choose. In this case, the function appears to be a cosine function because it starts at a maximum value (2 at [tex]\(x=0\)[/tex]).

With this information, we do not need a phase shift ([tex]\(C = 0\)[/tex]) as the cosine function typically peaks at [tex]\(x = 0\)[/tex].

Thus, combining all these values, we can construct the equation of the function. The general form of a cosine function with these parameters is:
[tex]\[ y = A \cos(B (x - C)) + D \][/tex]

Substituting the values we have found:
[tex]\[ y = 5 \cos\left(\frac{\pi}{6} x \right) + 2 \][/tex]

Therefore, a possible formula for the trigonometric function is:
[tex]\[ y = 5 \cos\left(\frac{\pi}{6} x \right) + 2 \][/tex]