Math Problem Statement

Find the graph of this function as the value of n increases, starting from n = 1: f(n) = (7/13 + (6/7)i)^n

Solution

The given function is:

f(n)=(713+67i)nf(n) = \left( \frac{7}{13} + \frac{6}{7}i \right)^n

This expression involves a complex number raised to the power of nn, where ii is the imaginary unit. Let's break this down:

  1. Complex Number Representation: The complex number here is z=713+67iz = \frac{7}{13} + \frac{6}{7}i. This number can be written in the form z=a+biz = a + bi, where a=713a = \frac{7}{13} and b=67b = \frac{6}{7}.

  2. Modulus and Argument: To analyze the behavior of f(n)f(n) as nn increases, we can compute the modulus and argument (polar form) of zz:

    • The modulus z|z| is given by z=a2+b2|z| = \sqrt{a^2 + b^2}.
    • The argument θ\theta is the angle of the complex number in the complex plane, given by θ=tan1(ba)\theta = \tan^{-1}\left(\frac{b}{a}\right).
  3. Repeated Powers of Complex Numbers: When raising a complex number to a power nn, its modulus gets raised to the power nn and the argument gets multiplied by nn. This means that the magnitude of the resulting number depends on zn|z|^n, and the angle rotates by nθn \theta as nn increases.

Visual Interpretation:

  • The images at the bottom show a pattern that resembles spirals or rotations in the complex plane. As nn increases, the points follow a path that increasingly circles around the origin.
  • These spirals result from the repeated multiplication of the complex number by itself, which creates a rotation (due to the argument θ\theta) and a possible shrinking or expanding (depending on the modulus z|z|).

Behavior as nn Increases:

  • The modulus z|z| will determine whether the points move towards the origin or away from it. If z<1|z| < 1, the points spiral inward, and if z>1|z| > 1, they spiral outward.
  • The rotation is governed by the argument θ\theta, creating circular patterns in the complex plane as seen in the provided graphs.

Would you like more details on any part of this analysis or have any specific questions about the function?

Here are five related questions:

  1. How is the polar form of a complex number used in analyzing powers of complex numbers?
  2. What is the significance of the modulus z|z| when raising a complex number to a power?
  3. How does the argument θ\theta affect the rotation of points in the complex plane?
  4. What happens to the shape of the graph if nn increases indefinitely?
  5. How do the real and imaginary parts of zz influence the structure of the graph?

Tip: When analyzing powers of complex numbers, the modulus tells you about the scaling (shrinking or expanding) effect, while the argument controls the rotation.

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Math Problem Analysis

Mathematical Concepts

Complex Numbers
Exponential Functions
Polar Coordinates
Modulus and Argument of Complex Numbers

Formulas

f(n) = (a + bi)^n
Modulus: |z| = sqrt(a^2 + b^2)
Argument: θ = tan^(-1)(b/a)

Theorems

Properties of Powers of Complex Numbers
Euler's Formula for Complex Numbers

Suitable Grade Level

Grades 10-12