A couple pretty easy integration problems im stuck on

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Discussion Overview

The discussion revolves around two integration problems involving partial fractions. Participants explore methods for integrating the functions 10/((x-1)(x^2+9)) and x^3/((x+1)^3), focusing on techniques such as partial fraction decomposition and substitution.

Discussion Character

  • Homework-related
  • Mathematical reasoning
  • Technical explanation

Main Points Raised

  • One participant suggests breaking down 10/((x-1)(x^2+9)) into partial fractions as 1/(x-1) - (x+1)/(x^2+9), proposing a solution involving logarithmic and arctangent functions.
  • Another participant provides a different result for the first integral, presenting ln|x+1| - 0.5ln|x^2+9| - 1/3*tan^-1(x/3) + C, indicating a variation in approach or calculation.
  • For the second integral, one participant describes performing long division and then applying partial fractions, yielding a solution involving logarithmic terms and rational functions.
  • A later reply mentions using substitution with u=x+1 for the second integral, suggesting an alternative method without detailing the outcome.

Areas of Agreement / Disagreement

Participants present differing results for the integrals, indicating that multiple approaches and solutions exist. There is no consensus on the final answers or methods used.

Contextual Notes

Some participants' solutions may depend on specific assumptions or methods, such as the choice of substitution or the handling of logarithmic terms. The discussion does not resolve these differences.

mathrocks
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integral of 10/((x-1)(x^2+9)) dx

integral of x^3/((x+1)^3) dx

both these are under the partial fraction section, so using those methods would be helpful...

thanks!
 
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The function 10/((x-1)(x^2+9) can be broken up into the partial fractions

1/(x-1) - (x+1)/(x^2+9)

The first one is simple (natural log of abs(denominator)). The second part is a bit more involved. I used trig substitution and worked through it. Use x=3*tan(theta).

When all is said there will most likely be more than one correct possible answer but the one I found is

ln(abs(x-1))-ln(Sqrt(x^2+9))-(1/3)*arctan(x/3) plus a constant.



For the second one the first thing I did was to do long division. This yielded

1- (3x^2+3x+1)/(x+1)^3

Next I worked out the partial fractions with the remainder that is left over from long division.

A/(x+1) + B/(x+1)^2 + c/(x+1)^3 = (3x^2+3x+1)/(x+1)^3

Some algebra (I like to equate the coefficients for this) yielded

A=3, B=-3 and C=1

Then do the integration on each section and you should get

x - 3*ln(abs(x+1)) - 3/(x+1) + 1/(2*(x+1)^2) plus a constant of course.
And if you take the derivative of this you will get back you integrand, which means you are correct.
 
Last edited:
I got... for the 1st one

ln|x+1|-0.5ln|x^2+9|-1/3*tan^-1(x/3)+C

2nd one...

x+1-3ln|x+1|-3/(x+1)-1/(2*(x+1)^2)+C

thats all I think...
 
I did substitution... and did u=x+1 and went from there for the 2nd one...
 

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