How Do You Separate Complex Equations into Real and Imaginary Parts?

In summary, the conversation discusses a problem where the goal is to write z^3 + 5z^2 = z + 3i as two real equations. The conversation includes attempts at solving the problem, with one person suggesting to expand and group the real and imaginary parts and another mentioning the need to use definitions.
  • #1
k3N70n
67
0

Homework Statement



Write [itex]z^3 + 5 z^2 = z + 3i[/itex] as two real equations

Homework Equations



z=a+bi?

The Attempt at a Solution



I've been just playing around with this. I expanded, grouped the real and imaginary parts. I'm really just think I'm groping around desperately in the dark.
I think I'm just missing something basic. Any hints would be greatly appreciated. Until then I'll be having a head butting contest with the sidewalk.
 
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  • #2
I would just expand out and group as well...as in the form z=A+Bi both A and B are real so...
 
  • #3
Okay.
So far I did this, I don't think there's any basic algebraic errors though it wouldn't be the first time.
[tex](a+bi)^3 + 5(a+bi)^2 = a + bi + 3i[/tex]
[tex]==> (a^3 +3 a^2 bi - 3ab^2-b^3 i) + (5a^2 +10abi-db^2) = a+bi+3i[/tex]
[tex]==> (a^3-3ab^2+5a^2-5b^2-a)+(3a^2b-b^3+10ab-b-3)i=0[/tex]
so somehow I have to use some mathematical magic to make that [itex]i[/itex] dissappear? Is this just a question that I need to play around with algebraically for a while?

Alright Kenton vs the Sidewalk round two
 
  • #4
Assuming you did that right, then x+iy=0 (for x and y real) only if x=0 and y=0. That's two real equations.
 
  • #5
And also you did not really need to bring everything over to one side to make it equal to zero. Remember that two complex numbers are equal iff their real and imaginary parts are the same.
 
  • #6
k3N70n said:
Okay.
So far I did this, I don't think there's any basic algebraic errors though it wouldn't be the first time.
[tex](a+bi)^3 + 5(a+bi)^2 = a + bi + 3i[/tex]
[tex]==> (a^3 +3 a^2 bi - 3ab^2-b^3 i) + (5a^2 +10abi-db^2) = a+bi+3i[/tex]
[tex]==> (a^3-3ab^2+5a^2-5b^2-a)+(3a^2b-b^3+10ab-b-3)i=0[/tex]
so somehow I have to use some mathematical magic to make that [itex]i[/itex] dissappear? Is this just a question that I need to play around with algebraically for a while?

Alright Kenton vs the Sidewalk round two
It's a problem where you need to know the definitions. Under what conditions on x and y is x+ iy= 0?
 

1. What is complex analysis?

Complex analysis is a branch of mathematics that deals with the study of complex numbers and their functions. It combines the ideas of calculus and algebra to analyze functions of complex variables.

2. What are complex numbers?

Complex numbers are numbers that can be expressed in the form a + bi, where a and b are real numbers and i is the imaginary unit (defined as the square root of -1). They have both a real and imaginary component.

3. What is the basic algebra of complex numbers?

The basic algebra of complex numbers includes addition, subtraction, multiplication, and division. Addition and subtraction are performed by combining the real and imaginary components separately. Multiplication is done using the distributive property and the fact that i² = -1. Division is done by multiplying the numerator and denominator by the complex conjugate of the denominator.

4. What are the main properties of complex numbers?

The main properties of complex numbers include commutativity and associativity of addition and multiplication, distributive property, existence of identity and inverse elements for addition and multiplication, and the fact that every non-zero complex number has a unique multiplicative inverse.

5. How is complex analysis used in real life?

Complex analysis has numerous applications in various fields such as physics, engineering, and economics. It is used to model and analyze systems that involve complex variables, such as electrical circuits, fluid dynamics, and quantum mechanics. It also has applications in signal processing, image processing, and financial analysis.

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