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# integration help watch

1. I am stuck with this. Initially, I thought I had to expand the brackets; to give me r^2-2r-8

But, that prove to be wrong. I am unsure as to what I am to do with the "r" term before the brackets, I thought that I would need to use that to form a cubic function, to give me r^3-2r^2+8r; but I am not entirely sure.
2. (Original post by apronedsamurai)

Originally
Multiply out the brackets then it is straightforward
3. (Original post by apronedsamurai)

I am stuck with this. Initially, I thought I had to expand the brackets; to give me r^2-2r-8

But, that prove to be wrong. I am unsure as to what I am to do with the "r" term before the brackets, I thought that I would need to use that to form a cubic function, to give me r^3-2r^2+8r; but I am not entirely sure.
It's -8r, and yes once you have the cubic function, integrate each term separately and don't forget the +C.
4. (Original post by apronedsamurai)

I am stuck with this. Initially, I thought I had to expand the brackets; to give me r^2-2r-8

But, that prove to be wrong. I am unsure as to what I am to do with the "r" term before the brackets, I thought that I would need to use that to form a cubic function, to give me r^3-2r^2+8r; but I am not entirely sure.
Have you got this now using the advice from the other posters and noting that your "+8r" should have been "-8r"?
5. r^3-2r^2-8r+c. Which integrates to;
1/4r^4-2/3r^3-4r^2+c

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Updated: January 15, 2015
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