# Help!!!

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#1
Hi, I'm unsure as to why -1/x+1 turns to (x-1)^-1 when it is being binomially expanded. Should it not be -1(x-1)^-1
Last edited by Username123455; 1 month ago
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1 month ago
#2
It's defo not (x-1)^-1 as it doesn't turn back into the original expression. I don't know how you got a negative 1 inside the bracket but the form you want it is -(1+x)^-1
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1 month ago
#3
Hi, I'm unsure as to why -1/x+1 turns to (x-1)^-1 when it is being binomially expanded. Should it not be -1(x-1)^-1
It doesn't! Can you post an image of the question you're attempting and any working or mark scheme solution?
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#4
(Original post by davros)
It doesn't! Can you post an image of the question you're attempting and any working or mark scheme solution?
https://pmt.physicsandmathstutor.com...l%20series.pdf

Question 1 and mark scheme is below. I divided it into partial fractions and then binomially expanded but mark scheme shows (x-1)^-1 must be used.
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1 month ago
#5
In question 1
-1/(x-1) turns into +(1-x)^(-1)
which is correct. They just multiplied the denominator by -1. This is different from what you posted.
Last edited by mqb2766; 1 month ago
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#6
(Original post by mqb2766)
In question 1
-1/(x-1) turns into +(1-x)^(-1)
which is correct. They just multiplied the denominator by -1. This is different from what you posted.
why is the denominator multiplied by -1 should it not be 1(x-1)^-1 divided by -1 to get -1(x-1)^-1
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1 month ago
#7
why is the denominator multiplied by -1 should it not be 1(x-1)^-1 divided by -1 to get -1(x-1)^-1

multiplying or dividing by -1 is the same. The correct expression is in the ms and #5.

In a binomial expansion, the "1" part is assumed to be positive, but you can expand 1-x just by replacing "x" in the expansion with "-x". Hence the need to multiply (x-1) by -1 to get (1-x)
Last edited by mqb2766; 1 month ago
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#8
(Original post by mqb2766)

multiplying or dividing by -1 is the same. The correct expression is in the ms and #5.

In a binomial expansion, the "1" part is assumed to be positive, but you can expand 1-x just by replacing "x" in the expansion with "-x". Hence the need to multiply (x-1) by -1 to get (1-x)
Thank you so much!
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