Partial Fractions Calc Problem

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Homework Help Overview

The problem involves evaluating the integral ∫1/[(x+a)(x+b)]dx using partial fractions. The original poster presents an expression for the integral and attempts to decompose the fraction into simpler components.

Discussion Character

  • Exploratory, Mathematical reasoning, Assumption checking

Approaches and Questions Raised

  • Participants discuss the decomposition of the integrand into partial fractions, questioning the values of constants A and B and their relationships. There is uncertainty about the correctness of the initial setup and the next steps in the integration process.

Discussion Status

Participants are actively engaging with the problem, with some providing guidance on the integral of 1/x and the implications of the relationship between A and B. There is a recognition of the need to clarify the values of A and B, but no consensus has been reached on the next steps.

Contextual Notes

There is an emphasis on the lack of numerical values for A and B, leading to discussions about their relationships rather than specific solutions. Participants are also considering the implications of the equation 1 = B(a-b) in their reasoning.

coookiemonste
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Homework Statement


∫1/[(x+a)(x+b)]dx
answer is 1/(a-b) ln[(x+b)/(x+a)] + C


Homework Equations





The Attempt at a Solution



1=A/(x+a) + B/(x+b)
1=B(x+a) + A(x+b)
1=Bx+ Ba + Ax +Ab

so 0=Bx+ Ax, 1=Ba+Ab
A=-B, 1=B(a-b)

∫-1/(x+a) +∫1/(x+b)

Im not sure if I am headed in the right direction or not.
 
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coookiemonste said:

The Attempt at a Solution



1=A/(x+a) + B/(x+b)

This line should really be 1/((x+a)(x+b))=A/(x+a) + B/(x+b)

1=B(x+a) + A(x+b)
1=Bx+ Ba + Ax +Ab

so 0=Bx+ Ax, 1=Ba+Ab
A=-B, 1=B(a-b)

Good, so B=___?

∫-1/(x+a) +∫1/(x+b)

Im not sure if I am headed in the right direction or not.

This should be B∫-1/(x+a) +B∫1/(x+b)
 
How do you know what A and B equal? You don't know numerical values, just what they're equal to in relation to one another.

gabbagabbahey is right, you should get B∫-1/(x+a) +B∫1/(x+b)

Now what do you know about the integral of 1/x ?
 
muso07 said:
How do you know what A and B equal? You don't know numerical values, just what they're equal to in relation to one another.
The equation 1= B(a-b) settles that.

gabbagabbahey is right, you should get B∫-1/(x+a) +B∫1/(x+b)

Now what do you know about the integral of 1/x ?
 

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