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# Quick factorising question watch

1. How would you factorise this equation?

2. Compare coefficients ?
See if something goes into it to give out 0 , ie factor theorem. Then compare the equation with (x+b)(Ax^2+Bx+C)

Or once you have the factor, polynomial division ?

Though I'm only at C2 so not sure if you're beyond that.
3. (Original post by puma21)
How would you factorise this equation?

With difficulty. There's one clean-ish root (i.e. one which doesn't involve surds), but it's not an integer so it would be quite hard to spot. What context has this question come up in? If it's A-level you'll never be asked to factorise something like this without being given one of the roots or factors already.
4. (Original post by nuodai)
With difficulty. There's one clean-ish root (i.e. one which doesn't involve surds), but it's not an integer so it would be quite hard to spot. What context has this question come up in? If it's A-level you'll never be asked to factorise something like this without being given one of the roots or factors already.
It's from a Step paper 2005, Q4. I know the answer from the mark scheme.
(2x - 1)(X^2 -16x - 11). But I want to figure out a way of solving it, I also tried comparing coefficients which was suggested but it requires some trial and error.
5. (Original post by nuodai)
With difficulty. There's one clean-ish root (i.e. one which doesn't involve surds), but it's not an integer so it would be quite hard to spot. What context has this question come up in? If it's A-level you'll never be asked to factorise something like this without being given one of the roots or factors already.
I disagree. Using factor theorem to factorise a cubic with this particular rational root is within the specification (the common roots are 1, -1, 2, -2, 3, -3, 0.5, -0.5).
6. (Original post by puma21)
It's from a Step paper 2005, Q4. I know the answer from the mark scheme.
(2x - 1)(X^2 -16x - 11). But I want to figure out a way of solving it, I also tried comparing coefficients which was suggested but it requires some trial and error.
You know the factor theorem and both 2 and 11 are prime ...
7. (Original post by Mr M)
I disagree. Using factor theorem to factorise a cubic with this particular rational root is within the specification (the common roots are 1, -1, 2, -2, 3, -3, 0.5, -0.5).
Oh fair enough; I just assumed it was for integer values of , but I never checked the specification.
8. Thanks for the help.
9. (Original post by puma21)
How would you factorise this equation?

10. (Original post by puma21)
How would you factorise this equation?

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Updated: March 29, 2011
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