Partial Fractions for Improper Fractions

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SUMMARY

The discussion focuses on integrating the improper fraction (x^3 + 72)/(x^2 + 6x + 8) using the method of partial fractions. Participants identified that the denominator factors into (x + 4)(x + 2), and the numerator's degree exceeds that of the denominator, necessitating polynomial long division before applying partial fractions. The correct approach involves dividing the polynomial first, leading to a result that includes a polynomial term alongside the logarithmic terms. The final answer incorporates both polynomial and logarithmic components, specifically -4*ln(x + 4) + 32*ln(x + 2) plus a polynomial term.

PREREQUISITES
  • Understanding of polynomial long division
  • Knowledge of partial fraction decomposition
  • Familiarity with logarithmic integration techniques
  • Basic algebraic manipulation skills
NEXT STEPS
  • Study polynomial long division techniques in detail
  • Learn about proper and improper fractions in calculus
  • Explore advanced integration techniques involving logarithms
  • Practice additional examples of partial fraction decomposition
USEFUL FOR

Students studying calculus, particularly those focusing on integration techniques, as well as educators seeking to clarify the application of partial fractions in improper fractions.

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Homework Statement



integrate((x^3+72)/(x^2+6x+8))dx

Homework Equations





The Attempt at a Solution



I decided to use partial fractions method.

x^2+6x+8 factors to (x+4)(x+2)

x^3+72=A(x+2)+B(x+4)

when A=-2, 64=B(2), B=32
when B=-4, 8=A(-2), A=-4

-4*int(1/(x+4)) + 32*int(1/(x+2))

-4*ln(x+4) + 32*ln(x+2) <---ANSWR

What was wrong?
 
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divide first
 
The numerator has higher degree than the denominator. Partial fractions only works on "proper fractions". As Mathgician said, divide first to get a polynomial plus a fraction. Then use partial fractions on that remaining fraction.
However, that still does NOT give -4*ln(x+4) + 32*ln(x+2) as the answer: there will be a (1/2)x2- 6x part. Is it possible you've miscopied the problem?
 

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