Writing Sine and Cosine Equations from Graphs

turksvids
1 Mar 201407:59
EducationalLearning
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TLDRThis educational video tutorial focuses on deriving the equations of sine and cosine functions from their graphs. It introduces the sinusoidal axis, amplitude, period, and phase shift, explaining how to identify these elements from a graph. The amplitude is the absolute value of 'a', found by the distance from the sinusoidal axis to the maximum or minimum. The period is calculated using 2Ο€ divided by 'B', and the phase shift is determined by the starting point 'C'. The video illustrates how to apply these concepts with examples, including handling unusual periods by counting multiple cycles and dividing. It also emphasizes the importance of recognizing the pattern of sine and cosine functions based on the sign of 'a', to correctly formulate the equations.

Takeaways
  • πŸ“š The video discusses how to find trigonometric equations for sine and cosine graphs.
  • πŸ” The general form of the equation is y = a * sin(B(x - C)) + D, where a, B, C, and D are constants.
  • πŸ“ The 'sinusal axis' (D) is found by looking at the midpoint of the graph's maximum and minimum values.
  • πŸ”‘ Amplitude (a) is the absolute value of a and can be found by calculating half the distance between the maximum and minimum of the graph.
  • πŸŒ€ The period of the graph is found by determining the length of one complete cycle and using the formula 2Ο€ / B.
  • πŸ”’ To find B, solve for it using the period of the graph, which is derived from the formula 2Ο€ / B.
  • πŸ“ The starting point (C) is chosen based on the x-intercept or can be given in the problem.
  • πŸ”„ The sign of a determines the pattern of the graph; if a > 0, it follows the pattern intercept-maximum-intercept-minimum, and if a < 0, it's the reverse.
  • πŸ“‰ For cosine, if a > 0, the graph starts at a maximum, and if a < 0, it starts at a minimum.
  • πŸ“ˆ The video includes examples of how to apply these concepts to a given graph to derive the equation.
  • πŸ”„ When the period is not straightforward, count multiple periods and divide to find the value of B, as demonstrated in the video.
Q & A
  • What is the general form of a trigonometric equation for sine and cosine functions?

    -The general form of a trigonometric equation for sine and cosine functions is y = a * sin(B * (x - c)) + d or y = a * cos(B * (x - c)) + d, where 'a' is the amplitude, 'B' determines the period, 'c' is the phase shift, and 'd' is the vertical shift.

  • What is the sinusoidal axis in the context of trigonometric graphs?

    -The sinusoidal axis, also known as the midline, is the horizontal line that represents the average value of the maximum and minimum of the sine or cosine function graph, which corresponds to 'd' in the equation y = a * sin(B * (x - c)) + d or y = a * cos(B * (x - c)) + d.

  • How do you find the amplitude of a sine or cosine function from its graph?

    -The amplitude is the absolute value of 'a' and can be found by calculating the distance from the sinusoidal axis to the maximum or minimum point of the graph, or by finding half the distance between the maximum and minimum points.

  • What is the formula to calculate the period of a sine or cosine function?

    -The period of a sine or cosine function is calculated using the formula 2Ο€ divided by the absolute value of 'B', which is 2Ο€/|B|.

  • How can you determine the value of 'B' from the graph of a sine or cosine function?

    -To determine 'B', you can measure the period of the function from the graph (the distance from one maximum to the next, or one minimum to the next), and then use the formula B = 2Ο€ / period.

  • What is the starting point 'c' in the equation of a sine or cosine function?

    -The starting point 'c' in the equation represents the phase shift of the function and is the value of 'x' where the function starts its cycle from an intercept.

  • How does the sign of 'a' affect the pattern of a sine or cosine graph?

    -If 'a' is positive, a sine graph will go from an intercept to a maximum to an intercept to a minimum, and a cosine graph will start at a maximum. If 'a' is negative, the patterns are reversed: sine goes from an intercept to a minimum to an intercept to a maximum, and cosine starts at a minimum.

  • What is the significance of the intercept in determining the starting point 'c' for a sine or cosine function?

    -The intercept is the point where the graph crosses the sinusoidal axis. It is used to determine the starting point 'c' because it indicates where the function begins its cycle.

  • How can you verify if the equation you derived for a sine or cosine graph is correct?

    -You can verify the derived equation by checking if moving over one full period (as calculated) brings you back to the starting point of the pattern, ensuring that the graph completes a full cycle.

  • What is an increment in the context of a sine or cosine function with a non-standard period?

    -An increment refers to the division of the period into equal parts, typically four, which helps in identifying the pattern of the function and in finding the correct starting points for different cycles.

  • Can you provide an example of how to find the sinusoidal axis from a given graph?

    -Yes, to find the sinusoidal axis, you can look at the graph and identify the average of the maximum and minimum values, or you can calculate it as (maximum + minimum) / 2.

Outlines
00:00
πŸ“š Introduction to Finding Trig Equations from Graphs

The video begins with an introduction to the process of deriving trigonometric equations, specifically sine and cosine, from their graphs. The general form of the equation is discussed, which includes the sinusoidal axis (y = D), amplitude (A), period (2Ο€/B), and phase shift (x = C). The amplitude is the absolute value of A and can be found by calculating the distance from the sinusoidal axis to the maximum or minimum points. The period is determined by the distance between two consecutive maximum or minimum points, and B is solved using the formula 2Ο€/B. The starting point or phase shift is identified as x = C. The video also discusses the significance of the sign of A in determining the pattern of the sine and cosine waves.

05:02
πŸ” Detailed Steps for Deriving Trigonometric Equations

This paragraph delves into the detailed steps for deriving the trigonometric equations from a given graph. It starts with identifying the sinusoidal axis, which can be found by averaging the maximum and minimum values of the graph. The amplitude is then calculated as the distance from the sinusoidal axis to the maximum or minimum points. The period is determined by counting the distance from one maximum or minimum to the next, or by counting the pattern of the graph. The formula for the period is 2Ο€/B, and B is solved accordingly. The phase shift is identified by the starting point on the y-axis. The video also explains how to adjust the equation for different starting points and patterns, including changing from sine to cosine and vice versa, by altering the sign and the starting point.

Mindmap
Keywords
πŸ’‘Trig Equations
Trig equations refer to mathematical equations involving trigonometric functions such as sine and cosine. In the context of the video, the focus is on finding the equations of sine and cosine given graphical representations. The script discusses the process of identifying key features of the graph to determine the parameters of the trigonometric equations, such as amplitude, period, and phase shift.
πŸ’‘Sine (sin)
Sine is a fundamental trigonometric function that relates the ratio of the lengths of the sides of a right triangle to the angles within that triangle. In the video, sine is used to describe the shape of the graph and to form the basis of the equations being discussed. The script mentions replacing 'S' with 'cosine' to switch between sine and cosine functions.
πŸ’‘Cosine (cos)
Cosine is another basic trigonometric function, often used alongside sine. It is also defined in relation to the angles and sides of a right triangle. The video script explains how to identify and write equations for cosine graphs by observing the graph's behavior and determining the sinusoidal axis, amplitude, period, and starting point.
πŸ’‘Sinusoidal Axis
The sinusoidal axis, also known as the midline, is the horizontal line that passes through the middle of a sine or cosine wave. It is defined as y equals D in the script, where D is the average of the maximum and minimum values of the graph. The sinusoidal axis helps in determining the vertical position of the wave on the graph.
πŸ’‘Amplitude
Amplitude in the context of trigonometry refers to the maximum distance from the sinusoidal axis to the peak (or trough) of a wave. It is represented by the absolute value of 'a' in the equation y = a*sin(B*(x-c)) + D. The script explains how to find the amplitude by looking at the maximum and minimum points on the graph or by calculating half the distance between them.
πŸ’‘Period
The period of a trigonometric function is the length of one complete cycle of the wave. In the script, the period is calculated using the formula 2Ο€/B, where B is a coefficient in the trigonometric function. The video demonstrates how to determine the period by observing the graph and counting the distance between successive maximum or minimum points.
πŸ’‘Phase Shift
Phase shift, denoted by 'c' in the script, is the horizontal shift of the wave from its standard position. It is an important parameter in the equation of a trigonometric function and can be determined by identifying the starting point of the wave on the x-axis. The video script explains how to find the phase shift by looking at the intercepts or the points where the wave crosses the sinusoidal axis.
πŸ’‘Starting Point
The starting point, or 'c' in the equation, is the x-coordinate where the wave begins its cycle. It is crucial for writing the complete equation of the trigonometric function. The script describes how to choose a starting point based on the graph's intercepts or by following the pattern of the wave.
πŸ’‘Increment
Increment in the script refers to the division of the period into equal parts, which helps in identifying the pattern of the wave and the phase shift. It is particularly useful when the period is not a simple value, as it allows for the calculation of the phase shift in more complex scenarios.
πŸ’‘Pattern Recognition
Pattern recognition in the context of the video is the ability to identify the repeating behavior of the sine or cosine wave. The script discusses how recognizing the pattern of the wave, such as going from an intercept to a maximum or minimum, helps in determining the sign of 'a' in the equation and the overall shape of the graph.
πŸ’‘Graph Analysis
Graph analysis is the process of examining the graphical representation of a function to extract information about its characteristics. In the video, graph analysis is used to find the sinusoidal axis, amplitude, period, and phase shift, which are then used to write the trigonometric equations. The script provides examples of how to perform this analysis on different types of sine and cosine graphs.
Highlights

Introduction to the process of finding trigonometric equations from graphs specifically for sine and cosine functions.

Explanation of the general form of a trigonometric equation: y = a * sin(B * (x - c)) + d.

Identification of the sinusoidal axis as y = D, which is the average of the maximum and minimum of the graph.

Amplitude is the absolute value of a and can be found using the distance from the sinusoidal axis to the maximum or minimum.

Period calculation using the formula 2Ο€ divided by B, where B is determined from the graph.

Method to find the period by counting from maximum to maximum or minimum to minimum, or by recognizing the pattern.

The importance of the starting point, x = c, in determining the phase shift of the trigonometric function.

Different patterns for sine and cosine based on the sign of a, affecting where the graph starts from an intercept or a maximum/minimum.

Demonstration of how to determine the sinusoidal axis, amplitude, period, and starting point using a given graph.

Using the graph to find specific values for D, amplitude, and period to construct the trigonometric equation.

Strategy for choosing starting points and adjusting the sign and function type (sine or cosine) based on the graph's pattern.

Example of how to adjust the equation when moving to different starting points on the graph.

Explanation of how to handle graphs with unusual periods by counting multiple periods and dividing.

Calculation of the increment per period to assist in finding starting points for different patterns on the graph.

Demonstration of constructing multiple equations for different starting points and verifying the correctness by completing the pattern.

Final review of the process and an encouragement for viewers to apply these methods to find equations for sine and cosine graphs.

Transcripts
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