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AS Maths: "Factorise the following equations and then sketch the curves" watch

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    I'm back!

    Right, I think I've done the first one right but I'm stuck with the other four.

    b) y = x^3 + 5x^2 + 4x

    = (x+0)(x+4)(x+1)?

    d) y = 3x + 2x^2 - x^3

    f) y = x - x^3

    h) y = x^3 - x^2 - 2x

    j) y = x^3 - 9x^2
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    first one is correct

    what are you stuck on with the other 4?
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    Yeah. What matt2k8 has said really and post some working along with it
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    Well for d:

    y = 3x + 2x^2 - x^3

    y = -x^3 + 2x^2 + 3x

    Then I can't factorise it from here? Or do I have to use the formula?
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    take out a power of x, so you have
    x(-x^2 + 2x + 3)
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    (Original post by Meleky)
    I'm back!

    Right, I think I've done the first one right but I'm stuck with the other four.

    b) y = x^3 + 5x^2 + 4x

    = (x+0)(x+4)(x+1)?

    d) y = 3x + 2x^2 - x^3

    f) y = x - x^3

    h) y = x^3 - x^2 - 2x

    j) y = x^3 - 9x^2
    for (d)(f)(h), just like you did with question (b), take out 'x' first
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    (Original post by mespannerhanz)
    take out a power of x, so you have
    x(-x^2 + 2x + 3)
    Then what? Brain is effing dead.
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    (Original post by Meleky)
    Then what? Brain is effing dead.
    Then factorise -x^2+2x+3. If it helps, write it as -(x^2-2x-3) and then factorise x^2-2x-3 (I find it easier this way).

    Each of these questions is the same: pull out common factors and then factorise what's left. If you can do one you should be able to do the rest.
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    (Original post by nuodai)
    Then factorise -x^2+2x+3. If it helps, write it as -(x^2-2x-3) and then factorise x^2-2x-3 (I find it easier this way).

    Each of these questions is the same: pull out common factors and then factorise what's left. If you can do one you should be able to do the rest.
    So (x+3)(x-1)(x+0)?

    And how comes you can just add a minus to everything? FFUU.
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    (Original post by Meleky)
    So (x+3)(x-1)(x+0)?

    And how comes you can just add a minus to everything? FFUU.
    be careful with + and -
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    (Original post by IAmTheChosenOne)
    be careful with + and -
    (x+3)(x-1)(0-x)?
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    (Original post by Meleky)
    So (x+3)(x-1)(x+0)?

    And how comes you can just add a minus to everything? FFUU.
    If you take a factor of -1 out then the signs get flipped. That is, a+b = -(-a-b).

    Now, factorising x^2-2x-3 should give (x-3)(x+1) and not (x+3)(x-1). As such, -x^2+2x+3 = -(x^2-2x-3) = -(x-3)(x+1).

    Also, when you're factorising things, you don't need to write x+0, you can write x.

    The answer in this case would therefore be -x(x-3)(x+1). To tidy it up a bit we can use the fact that -(x-3) = 3-x to write this as x(3-x)(x+1).

    Now you can do the rest. Remember:
    1. Take out common factors
    2. Factorise what's left (and if it's easier, take a factor of -1 out as well).
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    (Original post by nuodai)
    If you take a factor of -1 out then the signs get flipped. That is, a+b = -(-a-b).

    Now, factorising x^2-2x-3 should give (x-3)(x+1) and not (x+3)(x-1). As such, -x^2+2x+3 = -(x^2-2x-3) = -(x-3)(x+1).

    Also, when you're factorising things, you don't need to write x+0, you can write x.

    The answer in this case would therefore be -x(x-3)(x+1). To tidy it up a bit we can use the fact that -(x-3) = 3-x to write this as x(3-x)(x+1).

    Now you can do the rest. Remember:
    1. Take out common factors
    2. Factorise what's left (and if it's easier, take a factor of -1 out as well).
    You beautiful brute. Thanks so much.

    I'm now stuck with f though (y = x - x^3).

    I'm guessing you change it to y = -x^3 + x but then what?
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    (Original post by Meleky)
    You beautiful brute. Thanks so much.

    I'm now stuck with f though (y = x - x^3).

    I'm guessing you change it to y = -x^3 + x but then what?
    Common factors...
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    (Original post by Meleky)
    You beautiful brute. Thanks so much.

    I'm now stuck with f though (y = x - x^3).

    I'm guessing you change it to y = -x^3 + x but then what?
    Common factor of x, like all the others.
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    (Original post by nuodai)
    Common factors...
    y = -x^3 + x

    y = -x(x^2 - 1) or y = x(-x^2 + 1)?

    And then what?
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    Both expressions are the same
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    (Original post by Meleky)
    y = -x^3 + x

    y = -x(x^2 - 1)?

    Then what?
    Forgive my rudeness, but I can't tell if you're trolling or just have a really short memory. For the benefit of the doubt, I'll repeat what I said in my other post:
    1. Take out common factors
    2. Factorise what's left (and if it's easier, take a factor of -1 out as well).
    So what do you think is next?
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    (Original post by nuodai)
    Forgive my rudeness, but I can't tell if you're trolling or just have a really short memory. For the benefit of the doubt, I'll repeat what I said in my other post:

    So what do you think is next?
    I remember what you said, I just don't know how to "factorise what's left".
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    (Original post by Meleky)
    I remember what you said, I just don't know how to "factorise what's left".
    I'm fairly confident that you can factorise x^2-1 if you put your mind to it.
 
 
 

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