Mattyk's question at Yahoo Answers regarding local extrema

In summary, the function $f(x)=-2x^3+21x^2-36x+5$ has one local minimum at $x=1$ with a value of $-12$ and one local maximum at $x=6$ with a value of $113$. The link to this topic has been posted on Yahoo! Answers for the OP's reference.
  • #1
MarkFL
Gold Member
MHB
13,288
12
Here is the question:

Calculus homework help?!?

The function f(x) = -2 x^3 + 21 x^2 - 36 x + 5 has one local minimum and one local maximum.
This function has a local minimum at x equals ? with value ?
and a local maximum at x equals ? with value ?

Here is a link to the question:

Calculus homework help?!? - Yahoo! Answers

I have posted a link there to this topic so the OP can find my response.
 
Mathematics news on Phys.org
  • #2
Re: mattyk's question as Yahoo! Answers regarding local extrema

Hello mattyk,

We are given the function:

$f(x)=-2x^3+21x^2-36x+5$

To determine the critical values, i.e., the $x$-values at which the local extrema occur, we need to equate the first derivative to zero:

$f'(x)=-6x^2+42x-36=-6(x^2-7x+6)=-6(x-1)(x-6)=0$

Thus, our two critical values are:

$x=1,\,6$

To determine the nature of the extrema at these points, we may look at the sign of the second derivative there:

$f''(x)=-12x+42=-6(2x-7)$

$f''(1)>0$ thus $(1,f(1))=(1,-12)$ is a local minimum.

$f''(6)<0$ thus $(6,f(6))=(6,113)$ is a local maximum.
 

Related to Mattyk's question at Yahoo Answers regarding local extrema

1. What is a local extremum?

A local extremum is a point on a graph where the function reaches either a maximum or minimum value, and it is surrounded by values that are either higher or lower than itself.

2. How do you find local extrema on a graph?

To find local extrema on a graph, you can take the derivative of the function and set it equal to zero. The values of x where the derivative equals zero are potential local extrema. You can then use the second derivative test to determine if these points are local maxima or minima.

3. What is the difference between a local and global extremum?

A local extremum is a point where the function reaches a maximum or minimum within a specific interval, while a global extremum is the overall maximum or minimum of the entire function. A global extremum can occur at a local extremum, but not all local extrema are global.

4. Can a function have more than one local extremum?

Yes, a function can have multiple local extrema. A function can have both local maxima and minima, and there can be multiple of each type.

5. How are local extrema important in real-world applications?

Local extrema are important in real-world applications because they represent critical points in a function. For example, in economics and finance, local extrema can represent the highest and lowest points of a stock's price. In physics, local extrema can represent the maximum or minimum values of a physical quantity. Identifying and analyzing local extrema can provide valuable insights and help make informed decisions.

Similar threads

  • General Math
Replies
5
Views
915
Replies
1
Views
1K
  • Topology and Analysis
Replies
16
Views
1K
  • General Math
Replies
1
Views
11K
Replies
1
Views
2K
Replies
1
Views
2K
  • Topology and Analysis
Replies
9
Views
1K
Replies
7
Views
1K
Replies
1
Views
1K
Replies
1
Views
2K
Back
Top