Math Problem Statement

Consider the complex numbers z1=−6−6⋅i and z2=5−6⋅i. Find, giving your answers in the form a+b⋅i, where a,b∈R

:

a) 6⋅z1+3⋅z2=

b) 4⋅z1⋅z2=

c) z1z2=

Solution

Let's solve each part of the problem step by step.

Given:

  • z1=66iz_1 = -6 - 6i
  • z2=56iz_2 = 5 - 6i

Part (a): 6z1+3z26 \cdot z_1 + 3 \cdot z_2

First, calculate each term: 6z1=6(66i)=3636i6 \cdot z_1 = 6 \cdot (-6 - 6i) = -36 - 36i 3z2=3(56i)=1518i3 \cdot z_2 = 3 \cdot (5 - 6i) = 15 - 18i

Now, add them together: 6z1+3z2=(3636i)+(1518i)=2154i6 \cdot z_1 + 3 \cdot z_2 = (-36 - 36i) + (15 - 18i) = -21 - 54i

So, the answer to part (a) is: 2154i\boxed{-21 - 54i}

Part (b): 4z1z24 \cdot z_1 \cdot z_2

First, find the product z1z2z_1 \cdot z_2: z1z2=(66i)(56i)z_1 \cdot z_2 = (-6 - 6i) \cdot (5 - 6i)

Using the distributive property (FOIL): z1z2=(65)+(66i)+(6i5)+(6i6i)z_1 \cdot z_2 = (-6 \cdot 5) + (-6 \cdot -6i) + (-6i \cdot 5) + (-6i \cdot -6i) z1z2=30+36i30i+36i2z_1 \cdot z_2 = -30 + 36i - 30i + 36i^2

Since i2=1i^2 = -1: z1z2=30+6i+36(1)=30+6i36=66+6iz_1 \cdot z_2 = -30 + 6i + 36(-1) = -30 + 6i - 36 = -66 + 6i

Now, multiply this by 4: 4z1z2=4(66+6i)=264+24i4 \cdot z_1 \cdot z_2 = 4 \cdot (-66 + 6i) = -264 + 24i

So, the answer to part (b) is: 264+24i\boxed{-264 + 24i}

Part (c): z1z2\frac{z_1}{z_2}

To find the quotient z1z2\frac{z_1}{z_2}, multiply the numerator and denominator by the conjugate of the denominator:

Let z2=5+6iz_2^* = 5 + 6i (the conjugate of z2z_2).

z1z2=66i56i5+6i5+6i=(66i)(5+6i)(56i)(5+6i)\frac{z_1}{z_2} = \frac{-6 - 6i}{5 - 6i} \cdot \frac{5 + 6i}{5 + 6i} = \frac{(-6 - 6i)(5 + 6i)}{(5 - 6i)(5 + 6i)}

First, calculate the numerator: (66i)(5+6i)=3036i30i36i2=3066i+36=666i(-6 - 6i)(5 + 6i) = -30 - 36i - 30i - 36i^2 = -30 - 66i + 36 = 6 - 66i

Next, calculate the denominator: (56i)(5+6i)=25+30i30i36i2=25+36=61(5 - 6i)(5 + 6i) = 25 + 30i - 30i - 36i^2 = 25 + 36 = 61

Thus: z1z2=666i61=66166i61\frac{z_1}{z_2} = \frac{6 - 66i}{61} = \frac{6}{61} - \frac{66i}{61}

So, the answer to part (c) is: 66166i61\boxed{\frac{6}{61} - \frac{66i}{61}}

Summary of Answers:

a) 2154i-21 - 54i
b) 264+24i-264 + 24i
c) 66166i61\frac{6}{61} - \frac{66i}{61}

Would you like more details or have any other questions?

Here are 5 related questions:

  1. How do you multiply two complex numbers?
  2. What is the geometric interpretation of multiplying complex numbers?
  3. How do you find the conjugate of a complex number?
  4. Can you explain the process of dividing complex numbers using conjugates?
  5. What are the properties of the magnitude of a complex number?

Tip: When multiplying complex numbers, remember to treat i2i^2 as 1-1 to simplify your expressions.

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Math Problem Analysis

Mathematical Concepts

Complex Numbers

Formulas

Multiplication and Division of Complex Numbers

Theorems

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Suitable Grade Level

High School