Problem 17 - Advanced Engineering Mathematics

Question

Determine the order of the poles for the given function. \(f(z)=\tan z\)

Step-by-Step Solution

Answer

The poles of \( \tan z \) are of order 1 at \( z = \frac{\pi}{2} + n\pi \), where \( n \) is an integer.

Step 1: Understanding the Function

We need to determine the order of the poles of the function \( f(z) = \tan z \). The tangent function can be expressed as \( \tan z = \frac{\sin z}{\cos z} \). This expression indicates that \( f(z) \) will have poles where \( \cos z = 0 \).

Step 2: Locating the Poles

The cosine function \( \cos z \) is zero at the points \( z = \frac{\pi}{2} + n\pi \), where \( n \) is any integer. At these points, the denominator is zero and creates poles in the function \( \tan z \).

Step 3: Determining the Order of the Poles

To determine the order of the poles, examine the behavior of \( \tan z \) near \( z = \frac{\pi}{2} + n\pi \). Near these points, \( \cos z \) behaves linearly as it crosses zero. This indicates that \( \tan z \) behaves like \( \frac{1}{x} \), suggesting a simple pole (order 1).

Step 4: Conclusion

Therefore, the function \( f(z) = \tan z \) has simple poles (order 1) at \( z = \frac{\pi}{2} + n\pi \) for integer \( n \).

Key Concepts

Tangent Function

The tangent function is a fundamental concept in trigonometry and complex analysis. In its simplest form, the tangent of an angle in a right triangle is the ratio of the length of the opposite side to the adjacent side. However, in complex analysis, the tangent function is expressed as:\[\tan z = \frac{\sin z}{\cos z}\]This representation highlights its composition as the quotient of the sine and cosine functions. The properties of the tangent function are directly related to these trigonometric functions. A distinctive feature of \(\tan z\) is that it is undefined wherever \(\cos z = 0\). This aspect forms the basis for understanding poles of the function. The tangent function also has a periodic nature, repeating its values every \(\pi\) units along the real axis. This periodicity results in a series of regularly spaced poles, impacting the behavior of complex functions based on \(\tan z\).

Poles of a Function

In complex analysis, poles play a crucial role in understanding the behavior of meromorphic functions. A pole of a function is a specific type of singularity where the function approaches infinity at some point.

• A function \( f(z) \) has a pole at a point \( z_0 \) if \( f(z) \) goes to infinity as \( z \) approaches \( z_0 \).
• In the case of tangent function, \( \tan z = \frac{\sin z}{\cos z} \), poles occur where the cosine function, the denominator, equals zero.
• These zero points of \( \cos z \) correspond to poles of \( \tan z \), located at \( z = \frac{\pi}{2} + n\pi \).

Poles provide insights into the function's graph and its values. Understanding the location and nature of poles is essential for complex function analysis, particularly when integrating functions around contours or evaluating the residues at those poles.

Order of a Pole

The order of a pole is an important concept in complex analysis. It characterizes how a meromorphic function behaves near a singularity. Specifically, the order of a pole at \( z_0 \) is determined by how many times the function "blows up" or becomes infinite as it approaches \( z_0 \).

• A pole of order 1 is known as a simple pole. Here, the function resembles \( \frac{1}{(z-z_0)} \) near \( z_0 \).
• Higher-order poles like order 2 or 3, would behave like \( \frac{1}{(z-z_0)^2} \) or \( \frac{1}{(z-z_0)^3} \) respectively.
• For the tangent function \( \tan z \), the poles occur at \( z = \frac{\pi}{2} + n\pi \), and these are simple poles.

This means that near these points, \( \tan z \) experiences a vertical asymptote, reverting to infinity in a manner proportionate to \( \frac{1}{x} \). Recognizing the order helps in performing integrations or finding residues in complex analysis.