Finding equation for trigonometric function based on two points

In summary, there is not a unique cosine function that can be determined solely from two points. The general cosine function has multiple degrees of freedom that require at least one point for each to obtain a unique function. However, if the function is restricted to just compression and translation, a unique function can be found using the two given points by solving a system of equations.
  • #1
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Is there any standard way to do this? Specifically, I know the equation I'm looking for is a cosine function, and I know two points. Is there a way to find the equation of the cos function which has been translated and compressed given only these two points?
 
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  • #2
Unfortunately there's not a unique cosine function given only two points. A general cosine function is something like A*cos(Bx+C)+D, where all of the capital letters are degrees of freedom. You need at least one point for each degree of freedom to have a unique function.

If you want to restrict the function to only compression and translation you could consider a function of the form A*cos(x+B), in which case you could determine a unique one. If the two points are (x,y) and (w,z), then you have to solve the system of equations:

A*cos(x+B) = y ==> A = y*sec (x+B)
and
A*cos(w+B) = z ==> B = arccos(z/A) + w
 

1. What is the process for finding an equation for a trigonometric function based on two points?

The process for finding an equation for a trigonometric function based on two points involves first determining the period of the function, then using the two given points to set up a system of equations. These equations can then be solved to find the amplitude, phase shift, and vertical shift of the function. Finally, the equation can be written in the form f(x) = A sin(Bx + C) + D, where A, B, C, and D are the previously determined values.

2. How do I determine the period of a trigonometric function?

The period of a trigonometric function can be determined by finding the distance between two consecutive peaks or troughs. This is equal to 2π/B, where B is the coefficient of x in the function's equation.

3. Can I use any two points on a trigonometric function to find its equation?

No, the two points used must be on the same cycle of the function. This means that they should have the same y-value and a difference in x-values equal to the period of the function.

4. What if I am given more than two points?

If you are given more than two points, you can still use the same process to find the equation of the trigonometric function. However, it may be helpful to graph the points first to determine which ones are on the same cycle of the function.

5. Can I use this method for finding the equation of any trigonometric function?

Yes, this method can be used for any trigonometric function, including sine, cosine, and tangent. However, the process may vary slightly depending on the function and the given points.

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