What are complex functions and how can they be graphed?

In summary, the conversation discusses the different forms of representing complex numbers, including a+bi, r(cos(theta) + isin(theta)), and r*e^(i * theta). The latter is similar to using polar coordinates in the x-y plane to describe a point. The conversation also delves into the concept of complex functions and whether they can be graphed in 2 dimensions. It is determined that for functions with complex inputs, they would need to be graphed in 3 dimensions.
  • #1
madah12
326
1
I know that a complex number can be written in form of a+bi and r(cos(theta) + isin(theta))
but I don't understand the the representation of it as r*e^(i * theta) also
 
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  • #3
uhm so since I like things by examples tell me if I got it right
5+2i
in polar form its
5.4 (isin(tan^-1(2/5)+.cos(tan^-1(2/5)
and it could be written as 5.4e^(i*tan^-1(2/5))?
 
  • #4
Yeah! that's exactly right.

If you imagine that complex numbers are a position in the x-y plane, where the x-axis is real numbers and the y-axis is imaginary numbers; then a+ib is just a standard rectilinear (Cartesian) way of describing a point [e.g. 5+2i = 5x + 2y = (5,2) ]; when you use r*e^{i\theta}, its like writing it in polar coordinates, r is the magnitude, and theta the angle with the x-axis.
 
  • #5
zhermes said:
Yeah! that's exactly right.

If you imagine that complex numbers are a position in the x-y plane, where the x-axis is real numbers and the y-axis is imaginary numbers; then a+ib is just a standard rectilinear (Cartesian) way of describing a point [e.g. 5+2i = 5x + 2y = (5,2) ]; when you use r*e^{i\theta}, its like writing it in polar coordinates, r is the magnitude, and theta the angle with the x-axis.

is it possible with the rectangular coordinate to graph a complex function? I searched the net but couldn't figure out the right key words I mean like f(x)=2x+2ix and you input (2-i) and get 6+2i or does no such thing exist in mathematics?
 
  • #6
madah12 said:
I mean like f(x)=2x+2ix and you input (2-i) and get 6+2i or does no such thing exist in mathematics?
"Complex functions" are the general term for functions which operate on (or yield) complex numbers. But note, you have to input two scalars (the equivalent of a complex number)
[tex]
z = f(x+iy)
[\tex]
You, therefore, can't graph such functions in 2 dimensions, because you have 2 input dimensions (e.g. x and y) and then output dimensions (1 if your result is a real number, and 2 if your result is a complex number).

If you have a function which takes a complex number and gives a real number, you could plot it as a surface in 3 dimensions.
 

What is the polar form of a complex number?

The polar form of a complex number is a way of representing a complex number in terms of its magnitude (r) and angle (θ) from the positive real axis. It is written in the form r∠θ, where r is the modulus (distance from the origin to the complex number) and θ is the argument (angle between the positive real axis and the complex number).

How do you convert a complex number from rectangular form to polar form?

To convert a complex number from rectangular form (a + bi) to polar form (r∠θ), you can use the following formula: r = √(a² + b²), θ = tan⁻¹(b/a). This formula calculates the modulus and argument of the complex number, which can then be used to write it in polar form.

What is the relationship between the polar and rectangular forms of a complex number?

The polar and rectangular forms of a complex number are equivalent, meaning they represent the same complex number. The rectangular form is written as a + bi, where a and b are real numbers, while the polar form is written as r∠θ, where r is the modulus and θ is the argument. Both forms contain the same information about the complex number, just in different representations.

What is the advantage of using polar form over rectangular form for complex numbers?

The advantage of using polar form is that it makes it easier to perform certain operations on complex numbers, such as multiplication, division, and exponentiation. In polar form, these operations involve simply adding or subtracting angles and multiplying or dividing moduli, which is often simpler than using the algebraic rules for rectangular form.

How can polar form be used to graph complex numbers?

In polar form, the complex number r∠θ can be plotted on a polar coordinate plane, with r as the distance from the origin and θ as the angle from the positive real axis. This allows for a visual representation of the complex number and can be useful in understanding the properties of complex numbers, such as conjugates and roots.

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