Math Problem Statement

The graph of a sinusoidal function intersects its midline at [(0,2)] and then has a minimum point at [(3,-6)]. Write the formula of the function, where [x] is entered in radians.

Solution

The given information describes the characteristics of a sinusoidal function. Let the function be represented as:

f(x)=Asin(Bx+C)+Df(x) = A \sin(Bx + C) + D

where:

  • AA is the amplitude,
  • BB affects the period,
  • CC is the phase shift, and
  • DD is the vertical shift or the midline.

Step 1: Midline and Vertical Shift (DD)

The point (0,2)(0, 2) is where the function intersects its midline. Therefore, the midline is at y=2y = 2, which means:

D=2D = 2

Thus, the function becomes:

f(x)=Asin(Bx+C)+2f(x) = A \sin(Bx + C) + 2

Step 2: Amplitude (AA)

The minimum point of the function is at (3,6)(3, -6), and since the midline is y=2y = 2, the amplitude AA is the distance from the midline to the minimum point:

A=2(6)=8A = 2 - (-6) = 8

Therefore:

f(x)=8sin(Bx+C)+2f(x) = 8 \sin(Bx + C) + 2

Step 3: Period and BB

A sinusoidal function completes one full cycle in a specific period, which is given by:

Period=2πB\text{Period} = \frac{2\pi}{B}

The minimum point at (3,6)(3, -6) suggests that the quarter-period (from the midline to the minimum) is 3 units. Since the distance from the midline crossing to the minimum corresponds to a quarter of the period, we have:

Period4=3Period=12\frac{\text{Period}}{4} = 3 \quad \Rightarrow \quad \text{Period} = 12

Thus,

2πB=12B=π6\frac{2\pi}{B} = 12 \quad \Rightarrow \quad B = \frac{\pi}{6}

Step 4: Phase Shift (CC)

Since the function crosses the midline at x=0x = 0, there is no horizontal shift. Therefore, C=0C = 0.

Final Function

The function is now:

f(x)=8sin(π6x)+2f(x) = 8 \sin\left(\frac{\pi}{6}x\right) + 2

Conclusion

The formula of the sinusoidal function is:

f(x)=8sin(π6x)+2f(x) = 8 \sin\left(\frac{\pi}{6}x\right) + 2


Would you like further details on any of the steps? Here are 5 related questions for practice:

  1. How do you determine the phase shift of a sinusoidal function?
  2. What is the period of f(x)=3sin(π4x)+1f(x) = 3\sin\left(\frac{\pi}{4}x\right) + 1?
  3. How do you find the amplitude of a sinusoidal function from its graph?
  4. What effect does the coefficient BB have on the graph of a sine function?
  5. How would the function change if the minimum point was at (3,4)(3, -4) instead?

Tip: To quickly find the amplitude of a sinusoidal function, calculate the vertical distance between the midline and the maximum or minimum point.

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Math Problem Analysis

Mathematical Concepts

Trigonometry
Sinusoidal Functions
Amplitude
Period
Phase Shift
Vertical Shift

Formulas

f(x) = A sin(Bx + C) + D
Amplitude: A = |max - midline|
Period: Period = 2π / B
Phase shift: Horizontal shift determined by C
Midline: D is the vertical shift

Theorems

Properties of Sinusoidal Functions

Suitable Grade Level

Grades 10-12