Finding Extrema for (x-1)x^(2/3)

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    Extrema
In summary, to find the extrema for the function (x-1)x^(2/3), the derivative is first found to be (5x/3)^2/3 - 2/(3x^1/3). The critical numbers are then found by setting the derivative equal to zero and solving for x. The critical numbers are x=0 and x=2/5. The end points of the interval [0,1], which are x=0 and x=1, are also critical numbers. After plugging in these values, the extrema for the function are determined to be -0.32 as the absolute minimum and 0 as the absolute maximum.
  • #1
menal
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Homework Statement



i have to find the extrema for (x-1)x^(2/3)
so i found the derivative: (5x/3)^2/3 - 2/(3x^1/3)
now i have to find the critical numbers by putting the derivative equal to zero and solving for x...but i don't know how to do it.
are there even any roots?
 
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  • #2
So you have
[tex]\left(\frac{5x}{3}\right)^{2/3} - \frac{2}{3x^{1/3}}= 0[/itex]
If x= 0 then the last fraction is undefined (so x= 0 is a critical point), if not we can multiply through by [itex]3x^{1/3}[/itex]. What does that give you?
 
  • #3
if you plug in zero though, it becomes undefined, not 0...so how can that be a critical point? anddo you mean taking (5x-2)/(3x^1/3)
and since the bottom doesn't matter, jst find the zero of the top part (5x-2) and get 2/5?
would that be correct?
and the only root?
 
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  • #4
menal said:
if you plug in zero though, it becomes undefined, not 0...so how can that be a critical point? and do you mean taking (5x-2)/(3x^1/3)
and since the bottom doesn't matter, just find the zero of the top part (5x-2) and get 2/5?
would that be correct?
and the only root?
Review the definition of a critical number when finding extrema.
 
  • #5
oh! lol sorry. i ever knew that! so 0 is a critical number along with 2/5. that would be it?
 
  • #6
menal said:
oh! lol sorry. i ever knew that! so 0 is a critical number along with 2/5. that would be it?
How did you get 2/5?
 
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  • #7
"you mean taking (5x-2)/(3x^1/3)
and since the bottom doesn't matter, just find the zero of the top part (5x-2) and get 2/5"
 
  • #8
menal said:
"you mean taking (5x-2)/(3x^1/3)
and since the bottom doesn't matter, just find the zero of the top part (5x-2) and get 2/5"
Right. Now, use the critical numbers to find the extrema.
 
  • #9
yup! the interval given was (0,1)
so i plugged in 0,1 and 2/5 into the first equation:(x-1)x^(2/3)
and got 0,0 and -0.32
so my extreme values would be -0.32 as the absolute minimum and 0 as the absolute max.
 
  • #10
Was the interval (0,1), or was it [0,1] ?

Is x = 0 in your interval?
 
  • #11
[0,1]
 
  • #12
Look at both ends of the interval.
 
  • #13
you mean -2/5 would be one too?
 
  • #14
Of course. But when looking for extrema on a closed interval, you need to check each end of the interval for a possible extremum.
 
  • #15
so your sayin that -2/5 and 2/5 and then 7/5 (1 + 2/5) and 3/5 (1 - 2/5) would all be critical numbers.
 
  • #16
No.

If you're looking for extrema on the interval [0,1], the end points of the interval are also critical numbers. The end points are, x=0 (already a critical number) and x=1.

-2/5 is not in the interval [0,1] and not a critical number.
 
  • #17
yes, i have included 0 and 1 and 2/5 as my critical numbers already. I was just confused because i thought u were saying that i had to add/subtract the crticial number i got (2/5) from my intervals (0 and 1). But no, i think i get it now. the crticial numbers will be 0,1 and 2/5.
 
  • #18
Yes. 0, 2/5, and 1 .
 

1. What is the function for finding extrema for (x-1)x^(2/3)?

The function for finding extrema for (x-1)x^(2/3) is f(x) = (x-1)x^(2/3).

2. How do you find the extrema for (x-1)x^(2/3)?

To find the extrema for (x-1)x^(2/3), you can use the first derivative test or the second derivative test. The first derivative test involves finding the critical points of the function and testing them to see if they are local maxima or minima. The second derivative test involves finding the critical points and examining the concavity of the function at those points to determine if they are local maxima or minima.

3. What is the domain of (x-1)x^(2/3)?

The domain of (x-1)x^(2/3) is all real numbers except for x = 1, since the function is undefined at that point.

4. Can (x-1)x^(2/3) have more than one extrema?

Yes, (x-1)x^(2/3) can have more than one extrema. It can have both a local maximum and a local minimum, or it can have multiple local maxima or minima depending on the shape of the graph.

5. How do you graph (x-1)x^(2/3) to visualize the extrema?

To graph (x-1)x^(2/3), you can plot a few points and connect them to see the overall shape of the graph. You can also use a graphing calculator or software to plot the function and visualize the extrema. Additionally, you can find the critical points and plug them into the function to determine the exact coordinates of the extrema on the graph.

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