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Math Help - Factorizing

  1. #1
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    Factorizing

    I think the attachment sums it up...Where did I go wrong?
    Attached Thumbnails Attached Thumbnails Factorizing-factorizing.bmp  
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  2. #2
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    Hello

    Take heart. It was a good effort, it's 'nearly' correct.

    If you expand the factored expression what do you get? Can you see what to change?

    Hint: 4x - 3x = x
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  3. #3
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    Well...if I factor it I get the wrong solution. But I don't know what to change, I still don't know where I went wrong...
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  4. #4
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    Hello

    Use foil to expand the brackets

    (2x - 2)(x +3)

    What do you get?

    Now swap the 2 and the 3 and expand again. What do you get now, can you see why?
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  5. #5
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    why do you complicate...you can use determinant
    2x(squared)+x-6.......ax(squared)+b+c..a=2, b=1, c=-6
    d(stands for determinant cause i can't write its symbol)
    d=b(squared)-4ac
    d=1(squared)-4(2)(-6)
    d=1+48
    d=49
    square root(d)=7
    x1=(-b-(square root)d)/2a=(-1-7)/4=-8/4=-2
    x2=(-b+(squared root)d/2a=(-1+7)/4=6/4=3/2
    the factorization=(x-x1)(x-x2)=(x+2)(x-3/2)...you can change 3/2 and you will get
    (x+2)(2x-3)
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  6. #6
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    If you know how to factor when the coefficient of x^2 is one, here is the way to transform a quadratic equation with leading term not equal to one to quadratic equation with coefficient 1.

    2x^2+x-6=0

    Multiply by coefficient of x^2 (which is 2)
    4x^2+2x-6=0
    (2x)^2+2x-6=0

    Let a=2x, then the above is the same as
    a^2+a-6=0

    Now you should be able to factor it!!

    (a+3)(a-2)=0
    a=-3 or a=2
    2x=-3 ,2x=2
     x=-3/2 , x=1
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  7. #7
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    Quote Originally Posted by Ting View Post
    Hello

    Use foil to expand the brackets

    (2x - 2)(x + 3)

    What do you get?

    Now swap the 2 and the 3 and expand again. What do you get now, can you see why?
    My equation: 2x^2 + 4x - 6

    Having swapped the 2 and 3: 2x + x - 6

    But I still don't see where I'm wrong. I mean, I should be able to say "- 2x + 3x = b", where b is the "+x" in the middle of the equation, and I can. I don't see how I would tell that I'm wrong, and how to avoid the mistake in the future, short of expanding it again.
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  8. #8
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    My equation: 2x^2 + 4x - 6

    Having swapped the 2 and 3: 2x^2 + x - 6

    But I still don't see where I'm wrong. I mean, I should be able to say "- 2x + 3x = b", where b is the "+x" in the middle of the equation, and I can. I don't see how I would tell that I'm wrong, and how to avoid the mistake in the future, short of expanding it again.
    Hello

    It's good to see that you are trying to figure it out.

    When the coefficient of x^2 is 1 then you are correct, but you have 2x^2, so expanding.

    (2x - 2)(x + 3)

    2x^2 + 6x -2x -6

    b = 2*3 - 2 = 4

    Whereas

    (2x - 3)(x + 2)

    2x^2 + 4x -3x -6

    b = 2*2 - 3 = 1

    When the coefficient of x^2 is greater than 1 then one of the pair of factors of the constant term, c, will be multiplied by that coefficient. You have to consider that when finding which pair of factors, have a sum or difference equal to b.

    Is that any clearer?

    Try factoring some of these, maybe, to get the idea.

     2x^2 + 5x + 2

     3x^2 + 22x + 7

     3x^2 - 7x + 2
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  9. #9
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    Oh...so because the x^2 has a coefficient of 2, in factorising I should be multiplying the second coefficient by 2...
    If that makes sense. I think I understand.

    (2x - 2)(x + 3)
    Since -2 + 3 = 1, I figured I had it done. It matched the x coefficient. But I should've been doing -2 + 2*3 = 4, which is incorrect.

    And then for (2x - 3)(x + 2), I would do 2*2 - 3 which = 1, which is the correct coefficient.

    Thanks very much, I'm gunna go write that down.
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