Area of the region bounded between two curves with integration by parts

In summary, the conversation was about finding the area bounded between two curves using integration by parts. The integrand was \int34ln(x)-xln(x), with the lower bound being 1 and the upper bound being 34. After evaluating the integral, a mistake was found in the bounds which should have been from 1 to 34 instead of 0 to 34. The correct solution was then verified using a graphing calculator.
  • #1
maladroit
42
0

Homework Statement



Find the area bounded between the two curves
y=34ln(x) and y=xln(x)


Homework Equations



Integration by parts: [tex]\int[/tex]udv= uv-[tex]\int[/tex]vdu

The Attempt at a Solution


First I found the intersection points of the two equation to set the upper and lower bounds. The lower bound is 0 and the upper bound is 34. My integrand is as follows--

[tex]\int[/tex]34ln(x)-xln(x) with the limits of integration being from 0 to 34.

I evaluated the integral using integration by parts, and eventually came up with the following solution...

[tex]\int[/tex]34ln(x)-xln(x)= 34xln(x)-34x-(x[tex]^{2}[/tex]ln(x)/2) -(1/4)x[tex]^{2}[/tex]

and evaluated from 0 to 34, the answer is 1156ln(34)-1156-(1156ln(34)/2)+289

I am not quite sure where my mistake is being made. I verified my answer using a graphing calculator (although that does not absolutely make my answer correct), so if anyone sees where I am making my mistake I would greatly appreciate the help!
 
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  • #2
When you say the lower bound is 0, I don't see how that is possible. From your integral, it appears that you are integrating with respect to x. Neither of your functions is defined at x = 0.
 
  • #3
check this again

34xln(x)-34x-(xLaTeX Code: ^{2} ln(x)/2) -(1/4)xLaTeX Code: ^{2}

one of the sign is wrong
 
  • #4
My mistake was in the bounds, which should have been from 1 to 34. Thank you for your help!
 

1. What is the formula for finding the area of a region bounded between two curves?

The formula for finding the area of a region bounded between two curves using integration by parts is ∫(upper curve - lower curve)dx.

2. How do you determine the limits of integration for this type of problem?

The limits of integration are determined by finding the points of intersection between the two curves. These points will be the upper and lower bounds for the integral.

3. Can integration by parts be used for any type of bounded region?

No, integration by parts can only be used for regions bounded by two curves that intersect. If the region is bounded by more than two curves or the curves do not intersect, then a different method of integration must be used.

4. Is there a specific order in which the curves should be subtracted in the integral?

Yes, when using integration by parts, the upper curve should always be subtracted from the lower curve. This ensures that the area is calculated correctly and no negative values are obtained.

5. Are there any other methods for finding the area of a bounded region besides integration by parts?

Yes, other methods for finding the area of a bounded region include using basic geometry formulas, such as the area of a triangle or trapezoid, or using integration with respect to a single variable instead of two curves.

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