Chapter 17: Problem 16
In Problems 15-18, evaluate the given function at the indicated points. $$ f(z)=(x+1+1 / x)+i\left(4 x^{2}-2 y^{2}-4\right) $$ (a) \(1+i\) (b) \(2-i\) (c) \(1+4 i\)
Short Answer
Expert verified
(a) 3 - 2i, (b) 3.5 + 10i, (c) 3 - 32i.
Step by step solution
01
Understand the Function and Points
The given function is \( f(z) = (x+1+1/x) + i(4x^2 - 2y^2 - 4) \). Here, \( z = x + yi \) where \( x \) and \( y \) are real numbers representing the real and imaginary parts of \( z \). We need to evaluate this function for specific values of \( z \).
02
Evaluate at Point (a) 1+i
For \( z = 1+i \), \( x = 1 \) and \( y = 1 \). Substitute these into the function: \( f(1+i) = (1 + 1 + \frac{1}{1}) + i(4 \times 1^2 - 2 \times 1^2 - 4) \). Calculate the components: Real part: \( 1 + 1 + 1 = 3 \); Imaginary part: \( 4 - 2 - 4 = -2 \). Therefore, \( f(1+i) = 3 - 2i \).
03
Evaluate at Point (b) 2-i
For \( z = 2-i \), \( x = 2 \) and \( y = -1 \). Substitute these values: \( f(2-i) = (2 + 1 + \frac{1}{2}) + i(4 \times 2^2 - 2 \times (-1)^2 - 4) \). Calculate: Real part: \( 2 + 1 + 0.5 = 3.5 \); Imaginary part: \( 16 - 2 - 4 = 10 \). Thus, \( f(2-i) = 3.5 + 10i \).
04
Evaluate at Point (c) 1+4i
For \( z = 1 + 4i \), \( x = 1 \) and \( y = 4 \). Substitute these into the function: \( f(1+4i) = (1 + 1 + \frac{1}{1}) + i(4 \times 1^2 - 2 \times 4^2 - 4) \). Calculate: Real part: \( 1 + 1 + 1 = 3 \); Imaginary part: \( 4 - 32 - 4 = -32 \). Therefore, \( f(1+4i) = 3 - 32i \).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Complex Numbers
Complex numbers form an essential part of mathematics and are quite fascinating. A complex number is expressed as \( z = x + yi \), where \( x \) and \( y \) are real numbers. The variable \( i \) is known as the imaginary unit and is defined by the property \( i^2 = -1 \). This unique characteristic allows us to explore numbers beyond the traditional real number line.
- The real part of the complex number \( z \) is \( x \),
- The imaginary part is \( yi \).
Function Evaluation
Evaluating functions involving complex numbers is an important skill in complex analysis. For the given function \( f(z) = (x+1+1/x) + i(4x^2 - 2y^2 - 4) \), function evaluation involves substituting the given complex numbers into the function to find the resulting value.
First, identify the real \( x \) and imaginary \( y \) components from the complex number \( z = x + yi \). Substitute these values into both the real and imaginary parts of the function separately.
First, identify the real \( x \) and imaginary \( y \) components from the complex number \( z = x + yi \). Substitute these values into both the real and imaginary parts of the function separately.
- Calculate the real part: \( x+1+1/x \)
- Evaluate the imaginary component: \( 4x^2 - 2y^2 - 4 \)
Real and Imaginary Components
The expression of a function involving complex numbers often results in two components: a real part and an imaginary part. For instance, in our function \( f(z) = (x+1+1/x) + i(4x^2 - 2y^2 - 4) \), each part provides valuable insights into the behavior of the function.
The real component \((x+1+1/x)\) is processed by substituting \( x \) from the complex input \( z \). Meanwhile, the imaginary portion \(i(4x^2 - 2y^2 - 4)\) requires us to carefully substitute both \( x \) and \( y \), as both contribute to the result.
The real component \((x+1+1/x)\) is processed by substituting \( x \) from the complex input \( z \). Meanwhile, the imaginary portion \(i(4x^2 - 2y^2 - 4)\) requires us to carefully substitute both \( x \) and \( y \), as both contribute to the result.
- The real part affects the horizontal shift in the complex plane.
- The imaginary part influences the vertical displacement.