Math Problem Statement

z^4=(8-6i)^2

Solution

To solve the equation z4=(86i)2z^4 = (8 - 6i)^2, let's go step by step.

Step 1: Simplify the right-hand side

We need to simplify the expression (86i)2(8 - 6i)^2.

Using the formula for the square of a binomial: (ab)2=a22ab+b2(a - b)^2 = a^2 - 2ab + b^2 Let a=8a = 8 and b=6ib = 6i: (86i)2=82286i+(6i)2(8 - 6i)^2 = 8^2 - 2 \cdot 8 \cdot 6i + (6i)^2

First, compute the individual parts: 82=648^2 = 64 286i=96i-2 \cdot 8 \cdot 6i = -96i (6i)2=36(6i)^2 = -36

Now, put it all together: (86i)2=6496i36=2896i(8 - 6i)^2 = 64 - 96i - 36 = 28 - 96i

Step 2: Rewrite the equation

Now the equation becomes: z4=2896iz^4 = 28 - 96i

Step 3: Convert the right-hand side to polar form

We want to convert 2896i28 - 96i to polar form, as this will make finding the fourth roots easier.

First, calculate the magnitude (modulus) rr: r=282+(96)2=784+9216=10000=100r = \sqrt{28^2 + (-96)^2} = \sqrt{784 + 9216} = \sqrt{10000} = 100

Next, calculate the argument θ\theta. We use the formula: θ=tan1(9628)\theta = \text{tan}^{-1} \left( \frac{-96}{28} \right) θ=tan1(9628)=tan1(247)\theta = \text{tan}^{-1} \left( -\frac{96}{28} \right) = \text{tan}^{-1} \left( -\frac{24}{7} \right)

Using a calculator: θ1.2925radians\theta \approx -1.2925 \, \text{radians}

So, in polar form, we have: 2896i=100cis(1.2925)28 - 96i = 100 \text{cis}(-1.2925) where cis(θ)\text{cis}(\theta) is shorthand for cos(θ)+isin(θ)\cos(\theta) + i\sin(\theta).

Step 4: Take the fourth root

Now, we solve for zz. The equation is z4=100cis(1.2925)z^4 = 100 \text{cis}(-1.2925).

To find the fourth roots, we take the fourth root of the magnitude and divide the argument by 4. The magnitude of zz will be: z=1004=1001/4=10|z| = \sqrt[4]{100} = 100^{1/4} = \sqrt{10}

The argument for zz will be: 1.2925+2kπ4fork=0,1,2,3\frac{-1.2925 + 2k\pi}{4} \quad \text{for} \, k = 0, 1, 2, 3

Thus, the four solutions are: zk=10cis(1.2925+2kπ4)fork=0,1,2,3z_k = \sqrt{10} \, \text{cis} \left( \frac{-1.2925 + 2k\pi}{4} \right) \quad \text{for} \, k = 0, 1, 2, 3

These are the four values of zz.

Would you like more details on finding the exact angles or any part of this solution?

Here are some related questions:

  1. How do you convert complex numbers to polar form?
  2. What are the steps to compute the argument (angle) of a complex number?
  3. How do you find the roots of a complex number using De Moivre's Theorem?
  4. How do you handle negative arguments when solving roots of complex numbers?
  5. Can you express complex numbers in terms of Euler's formula?

Tip: When solving complex equations, converting numbers into polar form often simplifies root extraction and angle calculations.

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Math Problem Analysis

Mathematical Concepts

Complex Numbers
Polar Coordinates
Roots of Complex Numbers

Formulas

Square of a binomial: (a - b)^2 = a^2 - 2ab + b^2
Magnitude of a complex number: |z| = sqrt(a^2 + b^2)
Argument of a complex number: θ = tan^(-1)(b/a)
De Moivre's Theorem: z^n = r^n * cis(nθ)

Theorems

De Moivre's Theorem
Properties of Complex Numbers

Suitable Grade Level

Undergraduate or Advanced High School (Grades 11-12)