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Math Help - Factorising + Quadratics

  1. #1
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    Factorising + Quadratics

    Can anyone show me the way to solve this following equation by factorising, i need to see all workin out so i can fully understand, i've been pulling my hair out all day today. hope someone can help me.


    2xsquared -5x - 7 = 0


    Many Thanks
    Chris
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  2. #2
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  3. #3
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    Tried

    Quote Originally Posted by Peritus View Post
    I Have tried and struggle to understand it
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  4. #4
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    Quote Originally Posted by duckegg911 View Post
    Can anyone show me the way to solve this following equation by factorising, i need to see all workin out so i can fully understand, i've been pulling my hair out all day today. hope someone can help me.


    2xsquared -5x - 7 = 0


    Many Thanks
    Chris
    ok all u do is
    i think u have learnt how to factorise quadratics the same way i have.
    axsquared+bx+c
    a= 2 b=-5 c=-7
    a times c 2 times -7 is -14
    so now u have to list all the factors of -14 until u find a pair that adds up to b which is -5.
    1, -14
    2, -7
    7. -2
    14, -1
    2 plus -7 equals -5
    so.... now u do the rest
    can u remember it now? if u dont understand this way then i cant help u coz i have only learnt it like this, its possible maybe some1 else can help u tomorow
    Last edited by help_me; January 20th 2008 at 02:20 PM.
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  5. #5
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    Quote Originally Posted by duckegg911 View Post
    I Have tried and struggle to understand it
    these links might help:
    MyMaths.co.uk - factorisemovie
    and for more
    MyMaths.co.uk - factorise Higher
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  6. #6
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    Quote Originally Posted by help_me View Post
    ok all u do is
    i think u have learnt how to factorise quadratics the same way i have.
    axsquared+bx+c
    a= 2 b=-5 c=-7
    a times c 2 times -7 is -14
    so now u have to list all the factors of -14 until u find a pair that adds up to b which is -5.
    1, -14
    2, -7
    7. -2
    14, -1
    2 plus -7 equals -5
    so.... now u do the rest
    can u remember it now? if u dont understand this way then i cant help u coz i have only learnt it like this, its possible maybe some1 else can help u tomorow
    what year r u at school?
    Hey thats great, what comes next?
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  7. #7
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    Quote Originally Posted by duckegg911 View Post
    Hey thats great, what comes next?
    so u have found -14's factors u know that u have to find a pair that add up to b which equals -5
    2 and -7 add up to -5 so u put the pair into brackets such as

    (2x - 7)(x + 2) = 0
    then u expand the brackets
    as in 2xsquared+2x-7x-14
    then u simplify the equation into
    2xsquared-12x-7(check this bit im not entirely sure about this)
    hope it helps...............
    Last edited by help_me; January 20th 2008 at 02:41 PM. Reason: is this better?
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  8. #8
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    Quote Originally Posted by help_me View Post
    the links above will explain it far better than me try them first
    i totally understand your previous description, please try to explain the rest of the stages

    thanks
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  9. #9
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    Quote Originally Posted by help_me View Post
    so u put the pair in brackets

    (2x - 7)(x + 1) = 0
    then u expand them again
    as in 2xsquared+2x-7x-7
    then u simplify it down
    im sure u can do that
    the links above will explain it far better than me try them
    hope it helps...............
    Can you write the full solution as you would write it down ?
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  10. #10
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    Quote Originally Posted by duckegg911 View Post
    Can you write the full solution as you would write it down ?
    the answer is 2xsquared-12x-7
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  11. #11
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    Smile

    Quote Originally Posted by help_me View Post
    the answer is 2xsquared-12x-7
    Can anyone please confirm that this is infact the final answer?

    Many thanks
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  12. #12
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    answer

    Quote Originally Posted by duckegg911 View Post
    Can anyone please confirm that this is infact the final answer?

    Many thanks
    there is no more work required to solve the quadratic equation is there ?
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  13. #13
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    Quote Originally Posted by duckegg911 View Post
    there is no more work required to solve the quadratic equation is there ?
    So let's summarise:

    The start: SOLVE 2x^2 - 5x - 7 = 0

    Where you are now: You've factorised 2x^2 - 5x - 7 and got (2x - 7)(x + 1).

    (Note the typo in post #7)

    The finish: You have to SOLVE (2x - 7)(x + 1) = 0.

    In case you missed it, the key word in finishing the question is SOLVE:

    Either (2x - 7) = 0 \Rightarrow 2x = 7 \Rightarrow x = \frac{7}{2},

    Or (x + 1) = 0 \Rightarrow x = -1.

    So the SOLUTION to 2x^2 - 5x - 7 = 0 is x = \frac{7}{2}, \, -1.

    Now there's no more work required.
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