Chapter 3: Problem 64
The solutions of the equation \(z(\overline{z-2 i})=2(2+i)\) are (A) \(3+i, 3-i\) (B) \(1+3 i, 1-3 i\) (C) \(1+3 i, 1-i\) (D) \(1-3 i, 1+i\)
Short Answer
Expert verified
The solutions are \(-1+3i, -1-i\), which matches none of the given options.
Step by step solution
01
Understand the Problem
We are given the equation \(z(\overline{z-2i})=2(2+i)\) and need to find the correct solutions for \(z\). This involves dealing with complex numbers and their conjugates.
02
Rewrite the Equation
Substitute \(\overline{z-2i} \) with the conjugate of \(z-2i\), which is \(\overline{z} - 2i\). Thus the equation becomes \(z(\overline{z} - 2i) = 2(2+i)\).
03
Expand Left Side
Expand \(z(\overline{z} - 2i)\) to get \(z\overline{z} - 2iz\). The equation is now \(z\overline{z} - 2iz = 4 + 2i \).
04
Express z as a Complex Number
Let \(z = a + bi\), where \(a\) and \(b\) are real numbers. Then \(\overline{z} = a - bi\). Substitute these into the equation to get \((a + bi)(a - bi) - 2i(a + bi) = 4 + 2i \).
05
Simplify
Calculate \( (a + bi)(a - bi) \), which simplifies to \(a^2 + b^2\). Therefore, the equation becomes \(a^2 + b^2 - 2i(a + bi) = 4 + 2i\).
06
Separate Real and Imaginary Parts
Separate the equation into real part \(a^2 + b^2 - 2b = 4\) and imaginary part \(-2a = 2\).
07
Solve for Variables
From the imaginary part equation \(-2a = 2\), solve for \(a\). We get \(a = -1\). Substitute this into the real part equation \(a^2 + b^2 - 2b = 4\) to get \((-1)^2 + b^2 - 2b = 4\).
08
Simplify and Solve for b
Simplify the equation: \(1 + b^2 - 2b = 4\) becomes \(b^2 - 2b - 3 = 0\). Solve this quadratic equation to find \(b\).
09
Factorize Quadratic Equation
Factorize the quadratic \(b^2 - 2b - 3 = 0\) as \((b-3)(b+1) = 0\). The solutions are \(b = 3\) or \(b = -1\).
10
Find Solutions for z
Using \(a = -1\), the solutions for \(z\) are \(-1 + 3i\) and \(-1 - i\). Match these to the given options.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Quadratic Equations
Quadratic equations are a fundamental concept in mathematics, representing equations of the form \(ax^2 + bx + c = 0\). These equations are characterized by their degree, which is two, due to the highest exponent being squared. Solving a quadratic equation typically involves finding the values of \(x\) where the equation holds true.
Common methods for solving quadratic equations include:
Common methods for solving quadratic equations include:
- Factoring: Expressing the quadratic in a product form, such as \((x-p)(x-q) = 0\), where the solutions are \(x = p\) and \(x = q\).
- Using the Quadratic Formula: \(x = \frac{-b \pm \sqrt{b^2-4ac}}{2a}\), which gives the roots directly from the coefficients \(a\), \(b\), and \(c\).
- Completing the Square: Rewriting the quadratic in a square form \((x + d)^2 = e\), followed by solving for \(x\).
Conjugate of a Complex Number
When dealing with complex numbers, it's crucial to understand the concept of a conjugate. A conjugate of a complex number is derived by changing the sign of the imaginary part. For example, if \(z = a + bi\), then its conjugate \(\overline{z}\) is \(a - bi\).
The relevance of conjugates in mathematics includes:
The relevance of conjugates in mathematics includes:
- Simplifying Expressions: Products involving conjugates, such as \(z\overline{z}\), result in real numbers, specifically \(a^2 + b^2\).
- Division of Complex Numbers: Multiplying the numerator and the denominator by the conjugate of the denominator makes division feasible and simplifies the expression.
- Maintaining Equality: In equations involving complex numbers, where a solution requires equating both real and imaginary parts, conjugates help preserve balance and aid in simplification.
Imaginary and Real Parts
A complex number is composed of both real and imaginary parts. For a complex number represented as \(z = a + bi\), \(a\) is the real part and \(bi\) is the imaginary part, where \(b\) is a real coefficient and \(i\) is the imaginary unit defined by \(i^2 = -1\).
This breakdown of complex numbers into components has several practical applications:
This breakdown of complex numbers into components has several practical applications:
- Calculations and Operations: Operations on complex numbers—such as addition, subtraction, multiplication, and division—often require separating the parts for manipulation.
- Equating Components: When solving equations, separating the equation into real and imaginary parts amps up the solving process by treating each part independently.
- Visualization and Application: On the complex plane, the axes represent the real (horizontal) and imaginary (vertical) parts, aiding in visual comprehension and real-world applications like electrical engineering.