Satisfies Cauchy-Riemann equations but not differentiable

In summary, the conversation discusses the function f defined by f(z) = _z^2/z if z is not equal to 0 and 0 if z = 0. It is shown that f satisfies the Cauchy-Riemann equations at z = 0, but it is not differentiable there. To prove this, it is suggested to show that f'(0) does not exist by approaching 0 in two different ways and getting different results.
  • #1
ak123456
50
0

Homework Statement


Let f denote the function defined by
f(z)=
_z^2 /z if z is not 0
0 if z=0
show that f satisfies the Cauchy-Riemann equations at z=0 but that f is not differentiable there

Homework Equations





The Attempt at a Solution


it is easily to show the function satisfies Cauchy-Riemann equations
but how to show it is not differentiable
can i show f'(0) does not exist when z tends to 0 ?
 
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  • #2
_z is x-iy
 
  • #3
What you need to show is that f'(0) = lim_{h -> 0} ((f(h) - f(0))/h = lim_{h -> 0} _h^2/h^2. does not exist. To show that this limit does not exist, try approaching 0 in two different ways and show you get something different.
 

Related to Satisfies Cauchy-Riemann equations but not differentiable

1. What are the Cauchy-Riemann equations?

The Cauchy-Riemann equations are a set of partial differential equations that relate the real and imaginary components of a complex-valued function. They are used to determine if a function is differentiable, and if so, if it is analytic (meaning it has a power series representation).

2. How do the Cauchy-Riemann equations relate to differentiability?

The Cauchy-Riemann equations are necessary but not sufficient conditions for a function to be differentiable. This means that if a function satisfies the Cauchy-Riemann equations, it may be differentiable, but it also may not be. If a function does not satisfy the Cauchy-Riemann equations, it is not differentiable.

3. Can a function satisfy the Cauchy-Riemann equations but not be differentiable?

Yes, there are functions that satisfy the Cauchy-Riemann equations but are not differentiable. An example of such a function is the absolute value function, which is defined as f(x + iy) = |x + iy| = √(x^2 + y^2). This function satisfies the Cauchy-Riemann equations, but it is not differentiable at the point (0,0).

4. What does it mean for a function to be differentiable?

A function is differentiable if it has a well-defined derivative at every point in its domain. This means that the function's rate of change or slope can be determined at any point along its graph.

5. Can a function be differentiable without satisfying the Cauchy-Riemann equations?

No, a function cannot be differentiable without satisfying the Cauchy-Riemann equations. These equations are necessary for a function to be differentiable, but they are not sufficient. This means that if a function satisfies the Cauchy-Riemann equations, it may be differentiable, but if it does not satisfy them, it cannot be differentiable.

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