Finding the period of trig series analytically?

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Discussion Overview

The discussion revolves around calculating the period of trigonometric series analytically, specifically examining examples of functions composed of sine and cosine terms. The scope includes theoretical exploration and mathematical reasoning related to periodic functions.

Discussion Character

  • Exploratory
  • Mathematical reasoning

Main Points Raised

  • One participant asks if it is possible to calculate the period of a specific trigonometric series analytically.
  • Another participant suggests that the period can be derived from the individual terms, providing calculations for a specific example.
  • A different participant expresses confusion regarding the calculation of the period for another example, noting a discrepancy between analytical and graphical results.
  • One participant explains that the sum of two periodic functions is periodic if their periods are commensurable, detailing how to find the least common multiple of the individual periods.

Areas of Agreement / Disagreement

Participants express differing views on the calculation of periods, with some proposing analytical methods while others report conflicting graphical results. The discussion remains unresolved regarding the specific period calculations for the examples provided.

Contextual Notes

Participants mention the need for commensurability of periods and the concept of least common multiples, but there are unresolved aspects regarding the application of these concepts to specific examples.

gongo88
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Is there a way to calculate the period of a trigonometric series (like the one below) analytically?

x(t)=5sin(16t)-4cos(8t+3.1)
 
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The period in this case can be gotten from: 8t = 2π or t = π/4. This works since the other term has a period 16t = 2π or t = π/8 which is a harmonic.
 
Sorry, I'm still confused. For this example...

x(t)=4sin(15t)-3cos(9t+1.1)

...I have graphed this in MATLAB, and graphically found a period of about 2.1. I am trying to apply what you suggested, but can't figure out how to calculate the period of 2.1...
 

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The sum of two periodic functions will be periodic it the two periods are commensurable. That means the ratio of their periods is a rational number. And in that case, the period is the least common multiple of the individual periods. For non-integers p and q, the LCM is the least number z such that ap = z and bq = z for a and b integers.

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