One fundamental property of Fourier Series

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SUMMARY

The discussion centers on proving that the sum of two periodic functions, f(t) and g(t), is also periodic when the ratio of their periods P and Q is a rational number. Specifically, if P/Q can be expressed as m/n, where m and n are positive integers with GCD(m, n) = 1, then the combined function f(t) + g(t) is periodic with a period R, defined as R = (P/m) * LCM(m, n). This establishes that both f(x + R) and g(x + R) return to their original values, confirming the periodicity of the sum.

PREREQUISITES
  • Understanding of periodic functions and their properties
  • Knowledge of rational numbers and their representation
  • Familiarity with concepts of GCD (Greatest Common Divisor) and LCM (Least Common Multiple)
  • Basic grasp of Fourier Series and their applications
NEXT STEPS
  • Study the properties of periodic functions in depth
  • Learn about the applications of Fourier Series in signal processing
  • Explore the mathematical proofs involving GCD and LCM
  • Investigate the implications of periodicity in real-world systems
USEFUL FOR

Mathematicians, physicists, engineers, and students studying Fourier Series and periodic functions will benefit from this discussion.

viczhang
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Suppose the functions f(t) and g(t) are periodic with periods P and Q, respectively. If the ratio P/Q of their periods is a rational number, show that the sum f(t)+g(t) is a period function.

How to prove this?
 
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If their ratio is a rational number, it means it can be represented as:

[tex] \frac{P}{Q} = \frac{m}{n}, \; m, n \in \mathbb{Z}^{+}, \; \mathrm{GCD}(m, n) = 1[/tex]

Now, consider an interval of length:

[tex] R = \frac{P}{m}*\mathrm{LCM}(m, n)[/tex]

What can you say about [itex]f(x + R)[/itex] and [itex]g(x + R)[/itex]?
 

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