Solving an Integral Problem: Finding the Minus Sign

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Homework Statement (ignore what's written, it isn't important for the problem)I'm studying integrals and I came across this solved example. However I can't understand where the minus of the integral came from came from. Homework Equations The minus in the integral comes from the chain rule, specifically the derivative of ln(1-x). By making the substitution u = 1-x, the minus sign is accounted for in the anti-derivative.
  • #1
Jalo
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Homework Statement



2e2gumw.png

(ignore what's written, it isn't important for the problem)

I'm studying integrals and I came across this solved example. However I can't understand where the minus of the integral came from came from.

Homework Equations





The Attempt at a Solution



The primitive of a f^p * f ' function is f^(p+1) / (p+1) Therefore it should be ln^2(x-1)/2 and not -ln^2(x-1)/2

Thanks
 
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  • #2
You could dispel any doubts by making a u-substitution. Try [itex]u = 1 - x[/itex] and see where that takes you.
 
  • #3
Jalo said:

Homework Statement



2e2gumw.png

(ignore what's written, it isn't important for the problem)

I'm studying integrals and I came across this solved example. However I can't understand where the minus of the integral came from came from.

Homework Equations



The Attempt at a Solution



The primitive of a f^p * f ' function is f^(p+1) / (p+1) Therefore it should be ln^2(x-1)/2 and not -ln^2(x-1)/2

Thanks

By the chain rule: [itex]\displaystyle \frac{d}{dx}\ln(1-x)=\frac{1}{1-x}\frac{d}{dx}(1-x)=-\frac{1}{1-x}\,.[/itex]

So you have the anti-derivative of f^p * (- f ' ) .
 

FAQ: Solving an Integral Problem: Finding the Minus Sign

What is the purpose of solving an integral problem?

Solving an integral problem allows us to find the area under a curve, which is useful in many applications such as calculating volumes, work, or displacement.

How do I know if I need to include a minus sign when solving an integral?

If the function being integrated is negative over the interval of integration, then the integral will have a negative value. In this case, a minus sign must be included in the solution.

3. Can I simply ignore the minus sign and still get the correct answer?

No, the minus sign is an important part of the solution for an integral problem. Ignoring it will result in an incorrect answer.

4. Are there any specific techniques for finding the minus sign in an integral problem?

One technique is to draw a graph of the function and determine if the area under the curve falls below the x-axis. Another technique is to check the limits of integration and see if the function changes signs within those limits.

5. Why is it important to properly handle the minus sign in an integral problem?

Handling the minus sign correctly ensures that the solution is accurate and reflects the correct area under the curve. It also helps to avoid errors in further calculations or applications of the integral.

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