Find the period for a sine function that has a maximum at (pi/14,1) and a minimum at (3pi/14,-1) And write the equation: f(x) = sin ()

1 answer

To find the period of the sine function based on the given maximum and minimum points, let's first identify the properties of the sine function.

The standard sine function, \( f(x) = A \sin(B(x - C)) + D \), has:

  • A vertical shift determined by \( D \),
  • Amplitude given by \( A \),
  • A horizontal shift determined by \( C \),
  • A period given by \( \frac{2\pi}{B} \).

Step 1: Determine the period.

You provided a maximum at \( \left(\frac{\pi}{14}, 1\right) \) and a minimum at \( \left(\frac{3\pi}{14}, -1\right) \).

  • The distance between the maximum and minimum points is:

\[ \text{Distance} = \frac{3\pi}{14} - \frac{\pi}{14} = \frac{2\pi}{14} = \frac{\pi}{7} \]

In a sine function, the distance from a maximum to the next minimum is a quarter of the period (\( \frac{P}{4} \)), thus, we can setup the following equation for the period \( P \):

\[ \frac{P}{4} = \frac{\pi}{7} \]

Step 2: Solve for the period \( P \):

\[ P = 4 \cdot \frac{\pi}{7} = \frac{4\pi}{7} \]

Step 3: Write the equation of the sine function.

The maximum value is 1, which suggests the amplitude \( A = 1 \) (since sine ranges from -1 to 1), and the vertical shift \( D = 0 \). Since we need the function to have a maximum at \( x = \frac{\pi}{14} \), we need to adjust for the horizontal shift.

Considering a standard sine function has its first maximum at \( x = \frac{\pi}{2} \), we would typically need to shift it to the left to have it peak earlier.

Using the formula for the function, we have:

\[ f(x) = A \sin\left(B(x - C)\right) + D \]

Substituting our values \( A = 1 \), \( D = 0 \), \( P = \frac{4\pi}{7} \) gives us \( B \):

\[ B = \frac{2\pi}{P} = \frac{2\pi}{\frac{4\pi}{7}} = \frac{7}{2} \]

We need to find \( C \). Since the maximum occurs at \( x = \frac{\pi}{14} \), we can express \( C \) as follows:

\[ \text{Set } B\left(x - C\right) = \frac{\pi}{2} \text{ when } x = \frac{\pi}{14} \]

Thus,

\[ \frac{7}{2}\left(\frac{\pi}{14} - C\right) = \frac{\pi}{2} \]

Solving for \( C \):

\[ \frac{\pi}{14} - C = \frac{\pi}{7} \cdot \frac{2}{7} = \frac{\pi}{7} \cdot \frac{1}{4} = \frac{\pi}{2} \cdot \frac{1}{4} = \frac{\pi}{28} \] \[ C = \frac{\pi}{14} - \frac{\pi}{28} = \frac{2\pi}{28} - \frac{\pi}{28} = \frac{\pi}{28} \]

So, plugging it all into our equation, we get:

\[ f(x) = \sin\left(\frac{7}{2}\left(x - \frac{\pi}{28}\right)\right) \]

In conclusion, the function can be written as:

\[ f(x) = \sin\left(\frac{7}{2}x - \frac{7\pi}{56}\right) \]

This final equation represents the sine function with the specified maximum and minimum values.