Trigonometry - Trigonometric Graphs and Parameters

Trigonometry - Trigonometric Graphs and Parameters

TGM Original Questions

Consider the following definitions:

  1. Even Function : A function \(f(x)\) is an even function if for every \(x\) in its domain (the set of \(x\) where the function is defined on), the function satisfies the following equation:\[f(x) = f(-x).\] For example, \(f(x) = x^2\) is an even function, since for every real number \(x\), it satisfies that \(f(x) = x^2 = (-x)^2 = f(-x)\).
  2. Odd Function : A function \(f(x)\) is an odd function if for every \(x\) in its domain, the function satisfies the following equation: \[f(x) = -f(-x).\] For example, \(f(x) = x^3\) is an odd function, since for every real number \(x\), it satisfies that \(f(x) = x^3 = -(-x)^3 = -f(-x)\).
  3. Periodic Function : A function \(f(x)\) is a periodic function if there exists a positive number \(T\) such that, for every \(x\) in its domain, the function satisfies the following equation: \[f(x + T) = f(x),\] where the smallest positive number \(T\) is called the period of the function.
    For example, \(f(x) = \sin x + 2\) is a periodic function, since for every real number \(x\), there exists \(T = 2\pi\) such that, \[f(x) = \sin x + 2 = \sin(x + 2\pi) + 2 = f(x + 2\pi),\]where \(T = 2\pi\) is the period of \(f(x)\).

Using the definitions above, categorise the following functions:

  1. \(y = \sin 5x\)
  1. \(y = -4 \sin 2x + 3x\)
  1. \(y = \cos(\sin x)\)
  1. \(y = \tan 2x + 7x^5\)
  1. \(y = \sin 3x \sin 50x\)
  1. \(y = 1\)
  1. \(y = 2 \cos 6x - 1\)
  1. \(y = \cos 2x + x^2\)
  1. \(y = \sin(\cos x)\)
  1. \(y = \tan^2 3x\)
  1. \(y = x \cos 20x\)
  1. \(y = 0\)
  1. Even Function:
  2. Odd Function:
  3. Periodic Function:

Solution:

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Answer:Even: \(2\cos6x-1\), \(\cos2x+x^2\), \(\cos(\sin x)\), \(\sin(\cos x)\), \(\tan^2 3x\), \(\sin3x\sin50x\), \(1\), \(0\). Odd: \(\sin5x\), \(-4\sin2x+3x\), \(\tan2x+7x^5\), \(x\cos20x\), \(0\). Periodic under the stated existence criterion: \(\sin5x\), \(2\cos6x-1\), \(\cos(\sin x)\), \(\sin(\cos x)\), \(\tan^2 3x\), \(\sin3x\sin50x\), \(1\), \(0\). The two constant functions have no least positive period.

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