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how do you go from x-16x^1/2+15=0 to x^2+225=226x Watch

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    I dont get it.... here is the mark scheme

    http://qualifications.pearson.com/co...-June-2014.pdf

    question 8ii) and how they factorise it. I am really good at factorising and know the whole multiply co-efficient AC get two numbers that add to it. I don't understand this question though as there is no power of 2
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    Square both sides
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    (Original post by Blueberry.89)
    Square both sides
    squaring both sides hmm but what about the 16 X ^1/2 when you square that you get 16X? because of index laws? where does 226X come from? Sorry If I sound stupid
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    (Original post by Blueberry.89)
    Square both sides
    well my method would to tidy this up since X^y*X^Y=X^2y I can get rid of that half by replacing X^1/2 with y so now we have

    Y^2-16y+15=0 etc etc but then thats to get the value of X if I want to get from one side to the other like this then yes
    X+15=16x^1/2 squaring gives
    X^2+225=256X

    so maybe a mistake somewhere but no and here is why

    (X+15)(X+15)=x^2 +15x+15x+225
    =X^2+30x+225
    now (16^1/2)=256

    so
    X^2+30x+225=256x
    now
    x^2+225=256x-30x
    x^2+225=226x

    this may be a different way to explaining then how you explained it but this shows common mistakes people make and may be where he got confused.

    i deliberately make mistake at first to show how you can go wrong then show how it works broken down
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    (Original post by Luke7456)
    well my method would to tidy this up since X^y*X^Y=X^2y I can get rid of that half by replacing X^1/2 with y so now we have

    Y^2-16y+15=0 etc etc but then thats to get the value of X if I want to get from one side to the other like this then yes
    X+15=16x^1/2 squaring gives
    X^2+225=256X

    so maybe a mistake somewhere but no and here is why

    (X+15)(X+15)=x^2 +15x+15x+225
    =X^2+30x+225
    now (16^1/2)=256

    so
    X^2+30x+225=256x
    now
    x^2+225=256x-30x
    x^2+225=226x

    this may be a different way to explaining then how you explained it but this shows common mistakes people make and may be where he got confused.

    i deliberately make mistake at first to show how you can go wrong then show how it works broken down
    Thanks
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    (Original post by Emz99)
    I dont get it.... here is the mark scheme

    http://qualifications.pearson.com/co...-June-2014.pdf

    question 8ii) and how they factorise it. I am really good at factorising and know the whole multiply co-efficient AC get two numbers that add to it. I don't understand this question though as there is no power of 2
    NO SQUARING needed here

    (x0.5)2 - 16(x0.5) + 15 =0
    y2 -16y +15 =0


    Any good?
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    (Original post by ODES_PDES)
    NO SQUARING needed here

    (x0.5)2 - 16(x0.5) + 15 =0
    y2 -16y +15 =0


    Any good?
    Yes! you just let x^0.5 = y your awesome are you a teacher or something?
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    (Original post by Emz99)
    Yes! you just let x^0.5 = y your awesome are you a teacher or something?
    Just started my second year UNI
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    (Original post by ODES_PDES)
    Just started my second year UNI
    are you doing a maths degree? if so where at?
 
 
 
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