Chapter 2: Problem 53
For the following exercises, evaluate the expressions, writing the result as a simplified complex number. $$ \frac{(3+i)^{2}}{(1+2 i)^{2}} $$
Short Answer
Expert verified
The simplified complex number is
\(-2i\).
Step by step solution
01
Expand the Numerator
The expression for the numerator is \((3+i)^2 = (3+i) \times (3+i) = 9 + 3i + 3i + i^2 = 9 + 6i - 1 = 8 + 6i\). We used \(i^2 = -1\) for simplification.
02
Expand the Denominator
The expression for the denominator is \((1+2i)^2 = (1+2i) \times (1+2i) = 1 + 2i + 2i + 4i^2 = 1 + 4i + 4(-1) = 1 + 4i - 4 = -3 + 4i\). Again, notice \(i^2 = -1\).
03
Divide Complex Numbers
Now, divide the numerator by the denominator:\[ \frac{8+6i}{-3+4i}. \]To simplify, multiply the numerator and denominator by the conjugate of the denominator, \(-3-4i\).
04
Multiply by Conjugate
Multiplying by the conjugate gives:\[ \frac{(8 + 6i)(-3 - 4i)}{(-3+4i)(-3-4i)}. \]The denominator becomes \((-3)^2 - (4i)^2 = 9 + 16 = 25\).The numerator expands to \((8 \times -3) + (8 \times -4i) + (6i \times -3) + (6i \times -4i) = -24 - 32i - 18i - 24(-1) = 0 - 50i = -50i\).
05
Simplify the Result
The expression now is \(\frac{-50i}{25} = -2i\). Divide both the real and imaginary components by the denominator.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Complex Conjugate
In the realm of complex numbers, a **complex conjugate** is a key concept. It involves taking a complex number and changing the sign of its imaginary part while keeping the real part unchanged. For example, the complex conjugate of \(a + bi\) is \(a - bi\). This conjugate plays a vital role when dividing complex numbers, as multiplying a complex number by its conjugate results in a real number.
- Consider a complex number \(-3 + 4i\). Its conjugate is \(-3 - 4i\).
- The multiplication of a complex number with its conjugate, like \((a + bi)(a - bi)\), results in \(a^2 + b^2\).
Simplifying Complex Expressions
Simplifying complex expressions can be fun if you follow the right steps! When faced with a fraction of complex numbers, such as \(\frac{8+6i}{-3+4i}\), it's essential to simplify it into a standard form \(a + bi\). Here's a concise guide:
- First, ensure the expressions in both the numerator and the denominator are expanded and simplified separately.
- Use the conjugate of the denominator to help simplify the fraction. This will turn the denominator into a real number, easing the simplification process.
i Squared Rule
The **\(i^2\) rule** is a cornerstone in understanding complex numbers. Here’s why: the imaginary unit \(i\) is defined as the square root of \(-1\). With this definition comes a simple yet powerful rule: \(i^2 = -1\). This rule is crucial for simplifying expressions involving complex numbers.
- Whenever you see \(i^2\), replace it with \(-1\).
- This substitution helps convert complex expressions into a form that often involves only real numbers.