Math Problem Statement

Diketahui z1 = 2 − i, z2 = 2i, dan z3 = 1 − i. Operasi bilangan kompleks berikut yang benar adalah...

Solution

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Problem 5:

We are given three complex numbers:

  • z1=2iz_1 = 2 - i
  • z2=2iz_2 = 2i
  • z3=1iz_3 = 1 - i

We need to identify which operations among the options are correct:

  • Option A: z1+z2=2i+2i=2+iz_1 + z_2 = 2 - i + 2i = 2 + i. This is true.
  • Option B: z1z3=(2i)(1i)=2i1+i=1z_1 - z_3 = (2 - i) - (1 - i) = 2 - i - 1 + i = 1. This simplifies to just 1, so false.
  • Option C: z1×z2=(2i)×2i=2×2ii×2i=4i2i2=4i+2=2+4iz_1 \times z_2 = (2 - i) \times 2i = 2 \times 2i - i \times 2i = 4i - 2i^2 = 4i + 2 = 2 + 4i. This is false.
  • Option D: z2+z3=2i+(1i)=1+iz_2 + z_3 = 2i + (1 - i) = 1 + i. This is true.
  • Option E: z3×z1=(1i)(2i)=2i2i+i2=23i1=13iz_3 \times z_1 = (1 - i)(2 - i) = 2 - i - 2i + i^2 = 2 - 3i - 1 = 1 - 3i. This is true.

So, the correct options are A, D, and E.


Problem 6:

We are given the complex number z=33iz = -3 - 3i, and we need to determine which statements are correct:

  • Option A: The polar form of zz. First, we find the modulus and argument:

    • z=(3)2+(3)2=9+9=18=32|z| = \sqrt{(-3)^2 + (-3)^2} = \sqrt{9 + 9} = \sqrt{18} = 3\sqrt{2}.
    • The argument θ=tan1(33)=tan1(1)=45\theta = \tan^{-1}\left(\frac{-3}{-3}\right) = \tan^{-1}(1) = 45^\circ (but it's in the third quadrant, so 180+45=225180^\circ + 45^\circ = 225^\circ). Thus, the polar form is z=32(cos225+isin225)z = 3\sqrt{2}(\cos 225^\circ + i\sin 225^\circ), so false (the modulus in the statement is wrong).
  • Option B: Exponential form z=32ei225z = 3\sqrt{2}e^{i225^\circ}. This is true.

  • Option C: The complex number as an ordered pair z=(3,3)z = (-3, -3). This is true.

  • Option D: The conjugate zˉ=3+3i\bar{z} = -3 + 3i. This is true.

  • Option E: The principal argument arg(z)=135\arg(z) = 135^\circ. This is false; the correct argument is 225225^\circ.

So, the correct options are B, C, and D.


Would you like more details or further explanation on any of these answers?

Here are 5 related questions to help expand your understanding:

  1. How do you convert a complex number into polar form?
  2. What is the general process to find the argument of a complex number?
  3. How do you perform multiplication of two complex numbers?
  4. Why is the conjugate of a complex number important in mathematics?
  5. What are some applications of complex numbers in real-world problems?

Tip: Always remember to adjust the angle of a complex number based on its quadrant when finding the argument.

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Math Problem Analysis

Mathematical Concepts

Complex Numbers
Addition and Subtraction of Complex Numbers
Multiplication of Complex Numbers
Polar and Exponential Forms

Formulas

z1 + z2 = (a1 + b1i) + (a2 + b2i) = (a1 + a2) + (b1 + b2)i
z1 * z2 = (a1 + b1i)(a2 + b2i) = a1a2 + a1b2i + a2b1i + (b1b2)i^2

Theorems

Modulus of a complex number: |z| = sqrt(a^2 + b^2)
Argument of a complex number: Arg(z) = arctan(b/a)

Suitable Grade Level

Grades 11-12