2012 Year 9 &10 Mathematics Marathon (5 Viewers)

enoilgam · Sep 30, 2012

Fawun said:
do i square root it

Re-think the last line.

Fawun · Sep 30, 2012

enoilgam said:
Re-think the last line.

??

Was I not suppose to divide it by pi?

Demento1 · Sep 30, 2012

Fawun said:
do i square root it

Remember: You want to make 'r' the subject by itself.

Edit: No, he doesn't want you to square root it on the last line.

enoilgam · Sep 30, 2012

Fawun said:
??

Was I not suppose to divide it by pi?

Perhaps.

HSC2014 · Sep 30, 2012

3 pages later I think I may have to give up. :'( :'(
Edit: Fail whale, x = 5. I thought a maths question could always be tackled by manipulating the equation to get an answer. Who would've thought of 3,4,5 triangle seriously LOL..

Fawun · Sep 30, 2012

OMGZ I GOT IT~!!UYYGFSAFGJHSDGFJHSDGFSJD

c

Demento1 · Sep 30, 2012

Fawun said:
OMGZ I GOT IT~!!UYYGFSAFGJHSDGFJHSDGFSJD

Edit: BOS party at your house if you're correct.

Fawun · Sep 30, 2012

Fawun said:
OMGZ I GOT IT~!!UYYGFSAFGJHSDGFJHSDGFSJD

c

$\frac{1}{2}\pi r^2 = \pi r + 2r$

$\pi r^2 = 2\pi r + 4r$

$\pi r^2 = 2r (\pi + 2)$

$\frac{\pi r^2}{2r} = \pi + 2$

$\frac{\pi r}{2} = \pi + 2$

$\pi r = 2 \pi + 4$

$r = \frac{2 \pi + 4}{\pi}$

THANK YOU TO THE EPIPHANY THAT I JUST HAD

Sy123 · Sep 30, 2012

HSC2014 said:
3 pages later I think I may have to give up. :'( :'(
Edit: Fail whale, x = 5. I thought a maths question could always be tackled by manipulating the equation to get an answer. Who would've thought of 3,4,5 triangle seriously LOL..

Good job =)

enoilgam · Sep 30, 2012

Fawun said:
$\frac{1}{2}\pi r^2 = \pi r + 2r$

$\pi r^2 = 2\pi r + 4r$

$\pi r^2 = 2r (\pi + 2)$

$\frac{\pi r^2}{2r} = \pi + 2$

$\frac{\pi r}{2} = \pi + 2$

$\pi r = 2 \pi + 4$

$r = \frac{2 \pi + 4}{\pi}$

THANK YOU TO THE EPIPHANY THAT I JUST HAD

Thats it well done - you took a few more steps then necessary but still, you got there and thats what matters.

enoilgam · Sep 30, 2012

HSC2014 said:
3 pages later I think I may have to give up. :'( :'(
Edit: Fail whale, x = 5. I thought a maths question could always be tackled by manipulating the equation to get an answer. Who would've thought of 3,4,5 triangle seriously LOL..

Thats why I was sitting here thinking "why is this NOT WORKING". But anyway, its a great question I think - and truth be told it got me good. Thanks sy for your help.

Demento1 · Sep 30, 2012

Fawun said:
$\frac{1}{2}\pi r^2 = \pi r + 2r$

$\pi r^2 = 2\pi r + 4r$

$\pi r^2 = 2r (\pi + 2)$

$\frac{\pi r^2}{2r} = \pi + 2$

$\frac{\pi r}{2} = \pi + 2$

$\pi r = 2 \pi r+ 4$

$r = \frac{2 \pi + 4}{\pi}$

THANK YOU TO THE EPIPHANY THAT I JUST HAD

Alternatively, just a faster approach I found:

$\frac{1}{2}\pi r^2 = \pi r + 2r$

$\pi r^2 = 2\pi r + 4r$

$\pi r^2 = 2\pi r + 4r$

Now divide the equation on RHS by $\pi r$ , and you get:

$r = \frac{2 \pi + 4}{\pi}$

Edit: excuse my fail latexing. Typed it all wrong.

HSC2014 · Sep 30, 2012

Fawun you be levelling up

Fawun · Sep 30, 2012

enoilgam said:
Thats it well done - you took a few more steps then necessary but still, you got there and thats what matters.

I am happy lol I finally got ONE question right ITT

enoilgam · Sep 30, 2012

Fawun said:
I am happy lol I finally got ONE question right ITT

See, you're doing fine.

Fawun · Sep 30, 2012

Demento1 said:
Alternatively, just a faster approach I found:

$\frac{1}{2}\pi r^2 = \pi r + 2r$

$\pi r^2 = 2\pi r + 4r$

$\pi r^2 = 2\pi r + 4r$

Now divide the equation on RHS by $\pi r$ , and you get:

$r = \frac{2 \pi + 4}{\pi}$

idgi

my working out makes sense to me whereas yours doesn't lol

HSC2014 · Sep 30, 2012

Fawun said:
idgi

my working out makes sense to me whereas yours doesn't lol

With more experience you can see steps ahead of you that are redundant i.e. they just take up space. The markers will be able to see it too and so writing it out completely won't be necessary. It's like how mathematicians use the term 'clearly' in their solutions.

Fawun · Sep 30, 2012

^ and how do i acquire that experience

enoilgam · Sep 30, 2012

Fawun said:
^ and how do i acquire that experience

Practice mostly - experience in maths is so important (kind of like what you have been doing in this thread and by looking at demento's paper).

Demento1 · Sep 30, 2012

Fawun said:
idgi

my working out makes sense to me whereas yours doesn't lol

Nvm, I simplified it too quickly.

$\frac{1}{2}\pi r^2 = \pi r + 2r$

$\pi r^2 = 2\pi r + 4r$

$\pi r^2 = 2\pi r + 4r$

Now divide the equation on RHS by $\pi r$ , and you get:

$r = 2 + \frac{4}{\pi}$

Combine fractions.

$r = \frac{2 \pi + 4}{\pi}$

Ignore mine, to type it out, it's pretty much the same speed.

2012 Year 9 &10 Mathematics Marathon (5 Viewers)

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