The Student Room Group

Help with 12 (definitely not 11) in my pic

Anyone?:smile: thanks

Scroll to see replies

Reply 1
anyone?:/
Reply 2
How can you get rid of the root 2 on the rhs?
Reply 3
Original post by Matureb
How can you get rid of the root 2 on the rhs?


times the bottom and top of the fraction by root 2

what do I do after that?:/
(edited 11 years ago)
Reply 4
Original post by madfish
times the bottom and top of the fraction by root 2

what do I do after that?:/
Do that, then bring all x's to one side and factorise, then divide by the bracket for your solution. For simplification sake remember then x8=2x2x\sqrt 8=2x\sqrt 2 as another method and then divide by the coefficient given to your whole x term
(edited 11 years ago)
Reply 5
Or multiply everything by root 2. Then rearrange.
Reply 6
Original post by Robbie242
Do that, then bring all x's to one side and factorise, then divide by the bracket for your solution. For simplification sake remember then x8=2x2x\sqrt 8=2x\sqrt 2

how do we get it in the form they are looking?

edit, i got it :smile:

#thanks again robbiee
(edited 11 years ago)
Reply 7
Original post by madfish
how do we get it in the form they are looking?
11+3x2=2x211+\frac{3x}{\sqrt 2}=2x\sqrt 2 -> 11+3x22=2x211+\frac{3x\sqrt 2}{2}=2x\sqrt 2 therefore notice that 2x232x2=222x\sqrt 2 - \frac{3}{2}x\sqrt 2=\frac{\sqrt 2}{2} From here divide and rationalise
Reply 8
Original post by Robbie242
11+3x2=2x211+\frac{3x}{\sqrt 2}=2x\sqrt 2 -> 11+3x22=2x211+\frac{3x\sqrt 2}{2}=2x\sqrt 2 therefore notice that 2x232x2=222x\sqrt 2 - \frac{3}{2}x\sqrt 2=\frac{\sqrt 2}{2} From here divide and rationalise


yea i got it, thanks very much robbie :smile:
Reply 9
Original post by madfish
yea i got it, thanks very much robbie :smile:
No problem :biggrin:
Reply 10
Original post by Robbie242
No problem :biggrin:

How do we do 12 a?:/
Reply 11
Original post by madfish
How do we do 12 a?:/

Note that (xa)b=xab(x^a)^b=x^{ab} From this you can use your power to simplify them to ^3 and ^-3 Furthermore, set f(x)=5 then subtract 5 as it is on the end just leaving your x term accordingly, now you have a standard equation Solve it. (you may have to use inverse powers tell me when you get here)
Reply 12
Original post by Robbie242
Note that (xa)b=xab(x^a)^b=x^{ab} From this you can use your power to simplify them to ^3 and ^-3 Furthermore, set f(x)=5 then subtract 5 as it is on the end just leaving your x term accordingly, now you have a standard equation Solve it. (you may have to use inverse powers tell me when you get here)

i am up to (2x)^3=(3x)^-3

btw you are class at maths robbie... are your teachers not gutted you proved them wrong?:P
Reply 13
Original post by madfish
i am up to (2x)^3=(3x)^-3

btw you are class at maths robbie... are your teachers not gutted you proved them wrong?:P
Ok now this is how I'd do it this may seem a bit weird but its what I do
2x3=3x32x^3=\frac{3}{x^3} from this we notice that x^3 works well here, from this we can assert that 2x^6=3 therefore x6=32x^6=\frac{3}{2} I am going to put my method here as well to see if it works though, by substituion let x3=kx^3=k 2k=3/k2k=3/k-> 2k2=32k^2=3 k^2=3/2 so
Unparseable latex formula:

k=\sqrt \frac{3}{2}}

Don't forget plus or minus, similarly this means its true.

so solve x6=32x^6=\frac{3}{2} and I think you get the right answer. They aren't they're quite happy to see were topping league tables; selfish bastards
(edited 11 years ago)
Reply 14
Original post by Robbie242
Ok now this is how I'd do it this may seem a bit weird but its what I do
2x3=3x32x^3=\frac{3}{x^3} from this we notice that x^3 works well here, from this we can assert that 2x^6=3 therefore x6=32x^6=\frac{3}{2} I am going to put my method here as well to see if it works though, by substituion let x3=kx^3=k 2k=3/k2k=3/k-> 2k2=32k^2=3 k^2=3/2 so
Unparseable latex formula:

k=\sqrt \frac{3}{2}}

Don't forget plus or minus, similarly this means its true.

so solve x6=32x^6=\frac{3}{2} and I think you get the right answer. They aren't they're quite happy to see were topping league tables; selfish bastards

so we just take the 6th root of 3/2 ? how on earth we do that without a calculator?
Reply 15
Original post by madfish
so we just take the 6th root of 3/2 ? how on earth we do that without a calculator?
Seems a bit farfetched tbh, you could write it as x=326x=\sqrt[6]{\frac{3}{2}}
Reply 16
Original post by Robbie242
Seems a bit farfetched tbh, you could write it as x=326x=\sqrt[6]{\frac{3}{2}}


I know.. what a rotten question..

haha
Reply 17
Original post by madfish
I know.. what a rotten question..

haha
Am I right btw? I'm not sure haha
Reply 18
Original post by Robbie242
Am I right btw? I'm not sure haha


I don't think so but you are very close... the answer is 1.14 to 3dp according to my book
Reply 19
Original post by Robbie242
I don't think so but you are very close... the answer is 1.14 to 3dp according to my book


You should be taking the 6th root of 9/4, not 3/2~

Spoiler

(edited 11 years ago)

Quick Reply