Reverse diferentiation problem

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Homework Help Overview

The discussion revolves around a reverse differentiation problem involving the expression (x^2 + 3x - 1)/x^4. Participants are exploring the process of integrating this expression and addressing issues related to the manipulation of exponents.

Discussion Character

  • Exploratory, Mathematical reasoning, Problem interpretation

Approaches and Questions Raised

  • Participants discuss the steps involved in reverse differentiation, questioning the correctness of their exponent manipulations and the overall approach to integration. Some express confusion about the operations performed on the expression and seek clarification on the integration process.

Discussion Status

Several participants have provided insights into the integration process, noting the importance of correctly handling exponents and the operations involved. There is an acknowledgment of mistakes made in the initial attempts, and some participants are beginning to clarify their understanding of the integration steps.

Contextual Notes

There is a mention of potential confusion stemming from the original expression's format and the operations performed, particularly regarding the division by x^4 and the subsequent integration steps. Some participants suggest that clearer communication of the problem statement may aid in resolving misunderstandings.

cd246
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Homework Statement


(x^2+3x-1)/x^4 the answer is,(-x^-1)-(3/2)(x^-2)+(1/3)(x^-3)+C

Homework Equations


Just reverse diferentiation

The Attempt at a Solution


=x^2+3x-1+x^-4
=(x^3)/(3)+(3x^2)/(2)-x+(1/3)(x^-3+C)
(1/3)(x^3)+(3/2)(x^2)-x+(1/3)(x^-3)+C
I know i got the answer but somehow it is backwards(exponents mostly). What am I doing wrong?
 
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cd246 said:

Homework Statement


(x^2+3x-1)/x^4 the answer is,(-x^-1)-(3/2)(x^-2)+(1/3)(x^-3)+C

Homework Equations


Just reverse diferentiation

The Attempt at a Solution


=x^2+3x-1+x^-4
=(x^3)/(3)+(3x^2)/(2)-x+(1/3)(x^-3+C)
(1/3)(x^3)+(3/2)(x^2)-x+(1/3)(x^-3)+C
I know i got the answer but somehow it is backwards(exponents mostly). What am I doing wrong?
Look at your signs on the exponents before you intergrate and be careful, that should take care of it.
 
Remember in "backwards differentiation":
i) Exponent +1
ii) divide with the new exponent.

[tex](x^2+3x-1)/x^4 = x^{-2} + 3x^{-3} - x^{-4}[/tex]

the first term:
[tex]x^{-2} \rightarrow (x^{-2+1})/(-2+1) = -x^{-1}[/tex]
etc.
 
cd246 said:

Homework Statement


(x^2+3x-1)/x^4 the answer is,(-x^-1)-(3/2)(x^-2)+(1/3)(x^-3)+C


Homework Equations


Just reverse diferentiation


The Attempt at a Solution


=x^2+3x-1+x^-4
=(x^3)/(3)+(3x^2)/(2)-x+(1/3)(x^-3+C)
(1/3)(x^3)+(3/2)(x^2)-x+(1/3)(x^-3)+C
I know i got the answer but somehow it is backwards(exponents mostly). What am I doing wrong?

Perhaps it would help if you told us what the question is!

Are you trying to integrate (x^2+ 3x-1)/x^4?

You then write "= x^2+ 3x-1+ x^-4" which is not at all the same thing: you are adding x^-4 rather than dividing by x^4.

(x^2+ 3x- 1)/x^4= (x^2/x^4)+ 3(x/x^4)- 1/x^4= x^-2+ 3x^-3- x^-4.
Now integrate.
 
malawi_glenn said:
Remember in "backwards differentiation":
i) Exponent +1
ii) divide with the new exponent.

[tex](x^2+3x-1)/x^4 = x^{-2} + 3x^{-3} - x^{-4}[/tex]

the first term:
[tex]x^{-2} \rightarrow (x^{-2+1})/(-2+1) = -x^{-1}[/tex]
etc.

Now I know what I did wrong now, I just put x^-4 on top instead of subtracting the lower from the upper which I should have done. Thanks glenn
 

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