Math Problem Statement

Given the complex numbers z = -1 + 3i and w = 3 - i, find (a) |z̄w| and (b) Im(w/z).

Solution

Let's solve the problem given in the image:

You are provided with the complex numbers z=1+3iz = -1 + 3i and w=3iw = 3 - i.

Part (a) zˉw\left| \bar{z} w \right|

Here, zˉ\bar{z} is the complex conjugate of zz. The complex conjugate of z=1+3iz = -1 + 3i is zˉ=13i\bar{z} = -1 - 3i.

Now, we want to compute zˉw\left| \bar{z} w \right|.

  1. First, find the product zˉw\bar{z} w: zˉw=(13i)(3i)\bar{z} \cdot w = (-1 - 3i)(3 - i) Using the distributive property: = -3 + i - 9i + 3i^2$$ Since $$i^2 = -1$$, we substitute $$3i^2 = 3(-1) = -3$$: $$= -3 + i - 9i - 3 = -6 - 8i$$
  2. Now, compute the modulus zˉw\left| \bar{z} w \right|. For a complex number a+bia + bi, the modulus is: a+bi=a2+b2\left| a + bi \right| = \sqrt{a^2 + b^2} So, for 68i-6 - 8i: 68i=(6)2+(8)2=36+64=100=10\left| -6 - 8i \right| = \sqrt{(-6)^2 + (-8)^2} = \sqrt{36 + 64} = \sqrt{100} = 10

Thus, zˉw=10\left| \bar{z} w \right| = 10.

Part (b) Im(wz)\text{Im}\left( \frac{w}{z} \right)

We need to find the imaginary part of wz\frac{w}{z}.

  1. First, compute wz\frac{w}{z}. This is done by multiplying the numerator and the denominator by the complex conjugate of the denominator: wz=3i1+3i×13i13i\frac{w}{z} = \frac{3 - i}{-1 + 3i} \times \frac{-1 - 3i}{-1 - 3i} Simplify the numerator: = -3 - 9i + i + 3i^2 = -3 - 9i + i - 3 = -6 - 8i$$ Simplify the denominator: $$(-1 + 3i)(-1 - 3i) = (-1)^2 - (3i)^2 = 1 - 9(-1) = 1 + 9 = 10$$ So, $$\frac{w}{z} = \frac{-6 - 8i}{10} = -\frac{6}{10} - \frac{8}{10}i = -0.6 - 0.8i$$.
  2. The imaginary part of 0.60.8i-0.6 - 0.8i is 0.8-0.8.

Thus, Im(wz)=0.8\text{Im}\left( \frac{w}{z} \right) = -0.8.


Let me know if you need more details or have any questions!

Here are five related questions:

  1. How do you find the modulus of a complex number?
  2. What is the process for dividing complex numbers?
  3. What is the geometric meaning of the complex conjugate?
  4. Can you explain how to simplify the expression when multiplying complex numbers?
  5. How does the imaginary part affect the properties of a complex number?

Tip: Always express complex division in terms of multiplying by the conjugate to simplify the calculation.

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Math Problem Analysis

Mathematical Concepts

Complex Numbers
Modulus of Complex Numbers
Imaginary Part of Complex Numbers

Formulas

|a + bi| = √(a² + b²)
Complex Conjugate: z̄ = a - bi
Division of Complex Numbers: multiply by the conjugate

Theorems

Modulus Theorem
Division of Complex Numbers using Conjugates

Suitable Grade Level

Grades 10-12