Chapter 10: Problem 10
Let \(z=\ln (3)+j \pi / 2\) and \(a, b\) be real such that $$ a+j b=e^{z} $$ Determine \(a\) and \(b\).
Short Answer
Expert verified
a = 0, b = 3.
Step by step solution
01
Write the given complex number in exponential form
Given complex number is $$ z = \ln(3) + j \frac{\pi}{2} $$
02
Use Euler's formula to write exponential form
Euler's formula states that e^(x + jy) = e^x * (cos(y) + j\sin(y)).Apply this to the given z:$$ e^z = e^{\ln(3) + j \frac{\pi}{2}} = e^{\ln(3)} \cdot (cos(\frac{\pi}{2}) + j\sin(\frac{\pi}{2})) $$
03
Simplify the expression
First, simplify $$ e^{\ln(3)} = 3 $$Since cos(\frac{\pi}{2}) = 0 and sin(\frac{\pi}{2}) = 1, the expression becomes:$$ 3 \cdot (0 + j \cdot 1) = 3j $$
04
Identify real and imaginary parts
From the expression,$$a + jb = 0 + 3j $$Therefore, the real part a is 0 and the imaginary part b is 3.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Euler's formula
Euler's formula is a fundamental bridge between complex numbers and trigonometry. It states that for any real number \( x \) and \( y \), \[ e^{(x + jy)} = e^x \times (\text{cos}(y) + j\text{sin}(y)) \] This formula shows how exponential functions can map complex numbers, making it a powerful tool in many fields of science and engineering. Here's how it can be broken down:
- \( e^x \) represents the growth factor.
- The trigonometric functions, \( \text{cos}(y) \) and \( \text{sin}(y) \), describe rotation around the complex plane.
Exponential Form
The exponential form of a complex number is a way to express complex numbers in terms of their magnitude and angle. Using Euler's formula, any complex number \( z = a + jb \) can be written as: \[ z = e^{(x + jy)} \] Applying this to our problem, we have: \[ e^z = e^{\text{ln}(3) + j \frac{\text{Ï€}}{2}} \] Expanding this using Euler's formula provides: \[ e^{\text{ln}(3)} \times (\text{cos}(\frac{\text{Ï€}}{2}) + j\text{sin}(\frac{\text{Ï€}}{2})) \] Breaking it down:
- \( e^{\text{ln}(3)} = 3 \)
- The trigonometric parts: \( \text{cos}(\frac{\text{Ï€}}{2}) = 0 \) and \( \text{sin}(\frac{\text{Ï€}}{2}) = 1 \)
Imaginary Unit
The imaginary unit, represented by \( j \) (or sometimes \( i \) in mathematics), is a fundamental concept when working with complex numbers. It is defined by the property: \[ j^2 = -1 \] This allows complex numbers to be expressed in the form \( a + jb \), where \( a \) and \( b \) are real numbers. Here, \( a \) is the real part, and \( b \) is the imaginary part.When we say imaginary, it doesn't mean that it doesn't exist; instead, it represents values that can't be mapped directly onto the real line. In our problem, the presence of \( \text{ln}(3) + j \frac{\text{Ï€}}{2} \) means that the imaginary unit is being multiplied by \( \frac{\text{Ï€}}{2} \). By simplifying through Euler's formula and understanding the imaginary unit, we determine the complex number's real and imaginary parts effectively.
- The real part \( a = 0 \).
- The imaginary part \( b = 3 \).