# Thread: Integration of 1/(-x+1) and -1/(x-1): Why the different results?

1. ## Integration of 1/(-x+1) and -1/(x-1): Why the different results?

Both these integrals should yield the same result as -x+1 = -(x-1)

so 1/(-x+1) = 1/-(x-1)= -1/(x-1)

however one integrates to -ln(1-x) and the other to -ln(x-1)

x-1 is not equal to 1-x for all values except x = 1

so is the integral only defined for x = 1?

but it is possible to plot the integral over multiple values...

could someone please explain what is actually happening here..

thanks

2. Lacking additional information, $\int \dfrac{1}{x} dx = \ln(|x|) + C$

Does this modify your musings?

3. Thanks for the reply, but that wasn't my question.

It confuses me why moving the minus from the denominator to the numerator gives a different integral as the answer

-1/(x-1) integrates to -ln(x-1)

1/-(x-1) integrates to -ln(x-1)

x-1 is not equal to 1-x.

Why does this occur?

4. Originally Posted by anupjsebastian
Thanks for the reply, but that wasn't my question.

It confuses me why moving the minus from the denominator to the numerator gives a different integral as the answer

-1/(x-1) integrates to -ln(x-1)

1/-(x-1) integrates to -ln(x-1)

x-1 is not equal to 1-x.

Why does this occur?
How would the absolute value (pointed out in the first reply) affect these expressions?

5. Yeah makes sense with the absolute value... sorry my bad I didn't get the first reply.

thank you tkhunny and stapel .

#### Posting Permissions

• You may not post new threads
• You may not post replies
• You may not post attachments
• You may not edit your posts
•