Chapter 3: Problem 95
Divide as indicated. Write each quotient in standand form. $$\frac{9+2 i}{2+i}$$
Short Answer
Expert verified
The quotient in standard form is \(4 - i\).
Step by step solution
01
Understand the Problem
We need to divide the complex number \(9 + 2i\) by \(2 + i\) and express the result in standard form \(a + bi\).
02
Multiply by the Conjugate
To simplify this division, multiply the numerator and the denominator by the conjugate of the denominator \(2 - i\):\[\frac{9 + 2i}{2 + i} \cdot \frac{2 - i}{2 - i}\]
03
Simplify the Denominator
Using the identity \((a+b)(a-b) = a^2 - b^2\), calculate the denominator:\[(2+i)(2-i) = 2^2 - i^2 = 4 - (-1) = 5\]
04
Distribute in the Numerator
Now, distribute \(9 + 2i\) with \(2 - i\):\[(9 + 2i)(2 - i) = 9 \cdot 2 + 9 \cdot (-i) + 2i \cdot 2 + 2i \cdot (-i)\] Solve the individual terms to get:\[18 - 9i + 4i - 2i^2 = 18 - 9i + 4i + 2\] Using \(i^2 = -1\), this simplifies to:\[18 + 2 - 5i = 20 - 5i\]
05
Write the Result in Standard Form
Divide each term of the result by the denominator 5:\[\frac{20}{5} - \frac{5i}{5} = 4 - i\] Thus, the division results in the complex number \(4 - i\).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Complex Division
Dividing complex numbers is a bit different from dividing real numbers, but it follows a structured process that makes the operation straightforward. The goal is to find the quotient of two complex numbers. Just like in regular math, division can be seen as multiplying by a reciprocal. However, with complex numbers, we need to use the conjugate to perform this task.
Here’s what you do:
Here’s what you do:
- Identify the numerator and the denominator of the complex division problem.
- Multiply both the numerator and the denominator by the conjugate of the denominator.
- This multiplication clears the imaginary part of the denominator, effectively transforming it into a real number.
Standard Form
When we work with complex numbers, it is often helpful to express them in a standard form, which is given by the expression \(a + bi\). In this standard form, \(a\) is the real part, and \(b\) is the coefficient of the imaginary part \(i\).
Some key points about standard form:
Some key points about standard form:
- It clearly separates the real and imaginary components of the number.
- By maintaining this form, complex arithmetic remains consistent and understandable.
- This representation allows complex numbers to be plotted on a two-dimensional plane, enhancing visual understanding.
Conjugate
Conjugates play a crucial role in dividing complex numbers. The conjugate of a complex number is obtained by changing the sign of the imaginary part. For example, the conjugate of \(a + bi\) is \(a - bi\).
Here's why conjugates are important in complex division:
Here's why conjugates are important in complex division:
- They allow us to eliminate the imaginary unit \(i\) from the denominator.
- Multiplying a complex number by its conjugate results in a real number, specifically \(a^2 + b^2\).
- This property is used to "clean" the denominator, which simplifies the division process.