Derivative in the complex plane

In summary, the conversation is about differentiating a complex function, f(z)=2x^3+3iy^2, and finding its derivative, f '(x+ix^2). The person attempted to use partial differentiation with respect to x and y, but this is not the correct method for complex differentiation. The correct method involves using Cauchy-Reimann formulas, which the person realizes later on. The final answer should be 6x^2, as shown in the back of their textbook.
  • #1
cragar
2,552
3

Homework Statement


[itex] f(z)=2x^3+3iy^2 [/itex] then it wants
[itex] f '(x+ix^2) [/itex]

The Attempt at a Solution



So I take the partial with respect to x and i get
[itex] 6x^2 [/itex] then partial with respect to y and I get
6iy, then I plug in x for the real part and x-squared for the imaginary part,
then I get [itex] f ' (x+ix^2)=6x^2+6ix^2 [/itex]
the back of my book has [itex] f' = 6x^2 [/itex]
I don't see why its not what I got.
 
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  • #2
What do you know about complex differentiation? How is it defined? Which formulas do you know?
If you took the partial differentials, then this is not the complex differential. So why did you use them, i.e. how are they related?
 
  • #3
I know cauchy reimann formulas, so I did it wrong, first off it doesn't satisfy c-r formulas,
but for the imaginary part I should of taken the partial with respect to x as cauchy reimann implies, then that partial would be zero,
then the derivative would be 6x^2 .
 

Related to Derivative in the complex plane

1. What is a derivative in the complex plane?

A derivative in the complex plane is a mathematical concept that represents the instantaneous rate of change of a complex-valued function. It is similar to the derivative in the real plane, but in the complex plane, the derivative is a complex number rather than a real number.

2. How is the derivative in the complex plane calculated?

The derivative in the complex plane is calculated using a similar method as the derivative in the real plane. The formula for the derivative in the complex plane is f'(z) = lim (h → 0) [f(z + h) - f(z)]/h, where z is a complex number and h is a real number.

3. What is the significance of the derivative in the complex plane?

The derivative in the complex plane is significant because it allows us to understand the behavior of complex-valued functions. It helps us determine the rate of change of these functions at any point in the complex plane and also helps us find the maximum and minimum values of these functions.

4. Can a function have a derivative in the complex plane but not in the real plane?

Yes, it is possible for a function to have a derivative in the complex plane but not in the real plane. This happens when the function is not differentiable in the real plane, but it is differentiable in the complex plane. This can occur when the function has a singularity or a branch point in the real plane.

5. How is the concept of the derivative in the complex plane used in real-world applications?

The concept of the derivative in the complex plane is used in various real-world applications, such as engineering, physics, and economics. For example, it is used in signal processing to analyze and manipulate complex signals, in electrical engineering to study alternating currents, and in economics to understand the dynamics of complex economic systems.

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