Help finding the local min in a piecewise function

In summary, the conversation discusses finding the local minimum in a piecewise function. It is mentioned that the first derivative test was used, but there is uncertainty about its accuracy. It is also noted that the function has two possible values at x=0. The derivative of the first piece of the function is 0 at x=0, but the derivative of the second piece is never 0. This information leads to the conclusion that a local minimum may occur at x=-4, x=0, or x=4, but without knowing the value of f(0), it cannot be determined for sure.
  • #1
thinkbot
5
0
f(x) = {
{ 16 - x^2, if -4 <= x <= 0
{ 2x - 3, if 0 <= x <= 4
I did the first derivative test and got zero but i don't think that's right. Any help?
 
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  • #2
Re: Help finding the local min in a peicewise function

One quibble: \(\displaystyle f(0)\) has two values defined.

Do you find any critical values inside the two sub-domains?
 
  • #3
Re: Help finding the local min in a peicewise function

f^1(x)={2x
{2
0=2x x=0
thats what i had but i think its wrong
 
  • #4
Re: Help finding the local min in a peicewise function

thinkbot said:
f(x) = {
{ 16 - x^2, if -4 <= x <= 0
{ 2x - 3, if 0 <= x <= 4
I did the first derivative test and got zero but i don't think that's right. Any help?
As MarkFL pointed out, you can have f(0)= 16 or -3 but not both.

The derivative of [tex]16- x^2[/tex] is -2x which is 0 at x= 0 which is a "break point". Of course, the derivative of 2x- 3 is never 0.

That tells you that a local minimum must occur at x= -4, x= 0, or x= 4. Without knowing if f(0) is 16 or -3, we cannot say which or even if f has a local minimum.
 

1. How do I identify the piecewise function in my data?

In order to identify a piecewise function in your data, you will first need to look for any discontinuities or changes in the function's behavior. These changes will typically occur at specific values of the independent variable, such as a sharp turn or a sudden increase/decrease. Once you have identified these changes, you can then determine the different segments of the piecewise function.

2. How can I determine the local minima in a piecewise function?

The best way to determine the local minima in a piecewise function is to graph the function and visually identify where it reaches its lowest points. You can also take the derivative of the function and set it equal to zero, then solve for the independent variable to find the x-values of the local minima. Alternatively, you can use a graphing calculator or software to help you find the local minima.

3. Can a piecewise function have multiple local minima?

Yes, a piecewise function can have multiple local minima. This means that there can be multiple points in the function where the slope is equal to zero and the function reaches its lowest value. It is important to carefully examine the shape of the function and its different segments to identify all of the local minima.

4. Are there any specific techniques for finding the local minima in a piecewise function?

Yes, there are a few techniques that can be helpful in finding the local minima in a piecewise function. These include using the first or second derivative tests, graphing the function, or using a calculator or software to find the local minima. It is important to use multiple methods to verify the accuracy of your results.

5. Is it possible for a piecewise function to have no local minima?

Yes, it is possible for a piecewise function to have no local minima. This would occur when the function is either constantly increasing or constantly decreasing, and does not have any points where the slope is equal to zero. In this case, there are no local minima in the function.

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