Integral of (x-100)(.002e^(-.002*x))

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Homework Help Overview

The problem involves finding the integral of the function (x-100)(0.002e^(-0.002x)) from 100 to infinity. The context is within the subject area of calculus, specifically focusing on integration techniques.

Discussion Character

  • Exploratory, Mathematical reasoning, Problem interpretation

Approaches and Questions Raised

  • Participants discuss various integration methods, including integration by parts. There are attempts to clarify the steps taken in the integration process and identify where errors may have occurred. Questions arise regarding the correctness of the integration technique used and the calculations performed.

Discussion Status

The discussion is ongoing, with participants providing feedback on each other's calculations and suggesting corrections. Some participants express frustration over the complexity of the problem and the results obtained, indicating that multiple interpretations of the integration steps are being explored.

Contextual Notes

There is a noted discrepancy between the calculated result and the expected answer, prompting participants to question the setup and execution of the integration process. The discussion reflects a collaborative effort to identify and rectify misunderstandings in the calculations.

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Homework Statement

find the integral from 100 to infiniti for (x-100)(.002e^(-.002*x))



Homework Equations





The Attempt at a Solution

.(xe^-(.002x))(e^(-.002x))-(-100e^(-.002x)) |from 100 to infiniti = -(100e^-.2)(e^-.2)+100e^(-.2)=14.84
the answer should be 409.37. What am I missing, please?
 
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You didn't integrate it correctly. Post the details of your calculations so we can see where you went wrong.
 


(x-100)(.002e^(-.002*x))
I first multiplied out these two and got .002xe^(-.002x) - .2e^(-.002x). Then integrating the .002xe^(-.002x) I integrated the e part first and then the x part to get -xe^(-.002x) * e^(-.002x) and then I integrated the .2e^(-.002x) and got -100e^(-.002x).
 


The first integral you did is wrong. You need to do it by parts.
 


.002xe^(-.002x) - .2e^(-.002x). Ok. u=.002x du=dx
v= -(1/.002)e^(-.002x) dv=e^(-.002x)
so then, (.oo2x)(-(1/.002)e^(-.002x)- Integral of -(1/.002)e^(-.002x) dx from 100 to infiniti. (.oo2x)(-(1/.002)e^(-.002x) + (1/(.002*.002))e^(-.002x) from 100 to infiniti
0 - .2*(-409.3654)+(204682.69)==way wrong answer...Oh my goodness this is the ultimate in frustration...
 


Reformatted a bit to make it easier to read.
stevecallaway said:
0.002 x e^(-0.002x) - 0.2 e^(-0.002x)

u = 0.002x
du = dx
That's wrong. Fix this and the value for the first integral should come out okay.
dv = e^(-0.002x) dx
v = -(1/0.002) e^(-0.002x)

so then,

(0.002x)(-(1/0.002) e^(-0.002x) - Integral of -(1/0.002)e^(-0.002x) dx from 100 to infinity.
(0.002x)(-(1/0.002) e^(-0.002x) + (1/(0.002*0.002)) e^(-0.002x) from 100 to infinity
[0 - 0.2*(-409.3654)] + (204682.69) == way wrong answer

Oh my goodness this is the ultimate in frustration...
This is only the value of the first integral. You still need to do the integral of 0.2 e^(-0.002x).
 

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