Math Problem Statement

If 𝑧1 = 3 + 2𝑖 and 𝑧2 = 4 + 3𝑖. Find (i) 𝑧1𝑧2 (2 marks) (ii) 𝑧1 𝑧2 (2 marks)

Solution

Given the complex numbers z1=3+2iz_1 = 3 + 2i and z2=4+3iz_2 = 4 + 3i, let's find:

(i) z1z2z_1z_2 (2 marks)

To multiply two complex numbers, we use the distributive property:

z1z2=(3+2i)(4+3i)z_1z_2 = (3 + 2i)(4 + 3i)

Now, distribute the terms:

z1z2=3Γ—4+3Γ—3i+2iΓ—4+2iΓ—3iz_1z_2 = 3 \times 4 + 3 \times 3i + 2i \times 4 + 2i \times 3i

Simplifying each term:

z1z2=12+9i+8i+6i2z_1z_2 = 12 + 9i + 8i + 6i^2

Since i2=βˆ’1i^2 = -1:

z1z2=12+17i+6(βˆ’1)z_1z_2 = 12 + 17i + 6(-1)

z1z2=12+17iβˆ’6z_1z_2 = 12 + 17i - 6

z1z2=6+17iz_1z_2 = 6 + 17i

Answer for (i):

z1z2=6+17iz_1z_2 = 6 + 17i

(ii) z1z2\frac{z_1}{z_2} (2 marks)

To divide two complex numbers, multiply both the numerator and the denominator by the conjugate of the denominator:

z1z2=3+2i4+3iΓ—4βˆ’3i4βˆ’3i\frac{z_1}{z_2} = \frac{3 + 2i}{4 + 3i} \times \frac{4 - 3i}{4 - 3i}

This simplifies to:

z1z2=(3+2i)(4βˆ’3i)(4+3i)(4βˆ’3i)\frac{z_1}{z_2} = \frac{(3 + 2i)(4 - 3i)}{(4 + 3i)(4 - 3i)}

First, calculate the denominator using the difference of squares:

(4+3i)(4βˆ’3i)=42βˆ’(3i)2=16βˆ’9(βˆ’1)=16+9=25(4 + 3i)(4 - 3i) = 4^2 - (3i)^2 = 16 - 9(-1) = 16 + 9 = 25

Next, calculate the numerator:

(3+2i)(4βˆ’3i)=3Γ—4+3Γ—(βˆ’3i)+2iΓ—4+2iΓ—(βˆ’3i)(3 + 2i)(4 - 3i) = 3 \times 4 + 3 \times (-3i) + 2i \times 4 + 2i \times (-3i)

=12βˆ’9i+8iβˆ’6i2= 12 - 9i + 8i - 6i^2

Substitute i2=βˆ’1i^2 = -1:

=12βˆ’9i+8i+6=18βˆ’i= 12 - 9i + 8i + 6 = 18 - i

Now, divide by the denominator:

z1z2=18βˆ’i25=1825βˆ’125i\frac{z_1}{z_2} = \frac{18 - i}{25} = \frac{18}{25} - \frac{1}{25}i

Answer for (ii):

z1z2=1825βˆ’125i\frac{z_1}{z_2} = \frac{18}{25} - \frac{1}{25}i

Would you like more details or have any questions?


Here are five related questions:

  1. How do you find the modulus and argument of a complex number like z1z_1 or z2z_2?
  2. What is the geometric interpretation of the multiplication of complex numbers?
  3. How do you express the product z1z2z_1z_2 in polar form?
  4. What is the conjugate of a complex number, and how is it used in division?
  5. How do you add or subtract two complex numbers?

Tip: When dividing complex numbers, always multiply by the conjugate of the denominator to simplify the expression.

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Math Problem Analysis

Mathematical Concepts

Complex Numbers
Multiplication of Complex Numbers
Division of Complex Numbers

Formulas

Complex number multiplication formula
Complex number division using conjugate

Theorems

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Suitable Grade Level

Grades 11-12