Cosine Series Sketch and Calculate

In summary, The conversation revolved around a sketch of the Fourier Cosine series and whether it represented a periodic function. The expert questioned if the sketch was correct and if the function should be even since it is a sum of cosines. The person seeking help realized their mistake and corrected their sketch to show a periodic function with a period of -4 to 4.
  • #1
jegues
1,097
3

Homework Statement



See figure attached for problem statement as well as my attempt.

Homework Equations





The Attempt at a Solution



I'm not fully convinced I've done the sketch of the cosine series correctly or not, are there any mistakes?

Also, when solving for, [tex]a_{n}[/tex] I changed the n around so it would only contain the odd numbers.(it's 0 otherwise) Can I do this and have I done this correctly?

Thanks again!
 

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  • #2
jegues said:
I'm not fully convinced I've done the sketch of the cosine series correctly or not, ...

Me neither. Wouldn't a sum of cosines give an even function?
 
  • #3
LCKurtz said:
Me neither. Wouldn't a sum of cosines give an even function?

Hmmm... Then the sketch should look like this, correct?

See figure attached.
 

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  • #4
jegues said:
Hmmm... Then the sketch should look like this, correct?

See figure attached.

Is that sketch the graph of a periodic function?
 
  • #5
LCKurtz said:
Is that sketch the graph of a periodic function?

Well it says to sketch the Fourier Cosine series, the Fourier cosine series turns any function into a periodic function in terms of summations of cosines, right?
 
  • #6
jegues said:
Well it says to sketch the Fourier Cosine series, the Fourier cosine series turns any function into a periodic function in terms of summations of cosines, right?

Yes, it does. And you are supposed to sketch it. So I ask you again. Is your new sketch periodic?
 
  • #7
LCKurtz said:
Yes, it does. And you are supposed to sketch it. So I ask you again. Is your new sketch periodic?

I spotted my mistake now. Since my series is a cosine series my period is from -4 to 4, the sketch should be as follows.
 

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  • #8
jegues said:
I spotted my mistake now. Since my series is a cosine series my period is from -4 to 4, the sketch should be as follows.

Much better.
 

1. What is a cosine series sketch?

A cosine series sketch is a graphical representation of the cosine function, which is a trigonometric function that describes the relationship between the sides and angles of a right triangle. It is typically shown as a smooth, repetitive curve that oscillates between -1 and 1.

2. How is a cosine series calculated?

A cosine series is calculated using the Taylor series expansion of the cosine function. This involves breaking down the function into a sum of infinitely many terms, each of which is calculated based on the derivatives of the function at specific values. The more terms that are included in the series, the closer the approximation will be to the actual function.

3. What is the significance of a cosine series?

A cosine series has many applications in mathematics and physics. It is used to model periodic phenomena, such as sound waves and electromagnetic waves, and can also be used to approximate other functions. Additionally, the coefficients of a cosine series can reveal important information about the behavior of a function.

4. How does changing the number of terms affect a cosine series?

As mentioned earlier, the more terms that are included in a cosine series, the closer the approximation will be to the actual function. However, including too many terms can also lead to numerical errors and make the calculation more complex. Therefore, the number of terms used in a cosine series should be chosen carefully based on the desired level of accuracy and practical considerations.

5. Can a cosine series be used to represent any function?

No, a cosine series can only be used to approximate functions that are periodic and can be written as a sum of trigonometric functions. Functions that are not periodic or cannot be written in this form cannot be accurately represented by a cosine series.

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