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

1. 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
2. Square both sides
3. (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
4. (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
5. (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
6. (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?
7. (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?
8. (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
9. (Original post by ODES_PDES)
Just started my second year UNI
are you doing a maths degree? if so where at?

Updated: October 12, 2016
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