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Any1 get a sensible answer for question 12 a paper 2 - HSN forum

# Any1 get a sensible answer for question 12 a paper 2

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### #18139222014

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Posted 19 May 2006 - 02:27 PM

I did get an answer but that was from just making stuff up from the graph

### #2ScotlandGirl

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Posted 19 May 2006 - 02:28 PM

What was the question? I tried to block the exam out of my mind

### #3Vyka

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Posted 19 May 2006 - 02:33 PM

12 a) PS must be 6 - x from coordinates R and P. RS must be 12 - 8/x from coordinates R and P you can work this out.

so you get (6 - x)(12 - 8/x)

and from that you get A = 80 - 12x - 48/x

### #4ice_illusion

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Posted 19 May 2006 - 02:33 PM

I got 2 and -2 for the Xs but I'm pretty sure thats wrong since x has to be between 1 and 4. Can't remember what i got for the areas but one of them is wrong.

### #5loved-up-loon

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Posted 19 May 2006 - 02:34 PM

The last question?
I got something like 6-x and 12-8/x (cant remember what the exact numbers were) and I know these were right because when i used them for the area i got the one they gave you.
wooo thats some marks for me!
Grrrrrr!!

### #6ScotlandGirl

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Posted 19 May 2006 - 02:48 PM

QUOTE(ice_illusion @ May 19 2006, 03:33 PM)

I got 2 and -2 for the Xs but I'm pretty sure thats wrong since x has to be between 1 and 4.

At least 5 people I spoke too got -2 and 2, I did as well! We can't all be making the same mistake surely?!

### #7loved-up-loon

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Posted 19 May 2006 - 02:49 PM

Yeah i got 2 and -2 for the X's aswell!
Grrrrrr!!

### #8ice_illusion

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Posted 19 May 2006 - 02:53 PM

This what I think I should have done, although I'm not that sure.

b)
T.p when DA/dx=0

A = 80 - 12x - 48x^-1
DA/dx = -12 + 48x^-2
-12 + 48x^-2 = 0
48/x^2 = 12
48 = 12x^2
x^2 = 4
x = 2, -2
x cannot = -2

A = 80 - 12x - 48x^-1

A(2) = 80 - 12*2 - 48/2
= 32

A(1) = 80 - 12*1 - 48/1
= 20

A(4) = 80 - 12*4 - 48/4
= 20

And that gives areas of 65 and 20 which doesn't quite seem right. I'm sure it can't be both?
Whats wrong with that?
I didn't actually do it (just worked it out for 2,-2)
Edit: If it is exponential (sp?) then it won't have a turning point which explains why may nature table got the opposite of what I got when I put the numbers into the equation.
I divided by something instead of multiplying. So that makes it a miximum of 32 and a minimum of 20.

QUOTE(ScotlandGirl @ May 19 2006, 03:48 PM)

QUOTE(ice_illusion @ May 19 2006, 03:33 PM)

I got 2 and -2 for the Xs but I'm pretty sure thats wrong since x has to be between 1 and 4.

At least 5 people I spoke too got -2 and 2, I did as well! We can't all be making the same mistake surely?!

It says
"P lies on the curve with equation y = 8/6 between (1,8) and (4,2)"
That means it must have boundries and x can only equal something between 1 and 4. Also, the curve doesn't look like it ever goes across the y axis. I think it's just going to increase exponentially without ever going negative. I hope I'm wrong about that though.

### #9SncZ

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Posted 19 May 2006 - 02:55 PM

i dunno, how can you lot keep talking about it... its depressing :/

altho i did get the x =2,-2 aswell.....

### #10snowboardin_chik_5

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Posted 19 May 2006 - 03:12 PM

I gt x= -2 and 2 as well
the max area was 128 and the min was 32
I thot the paper could hav been alot worse but im plezd with the exam. Hopefully iv gt wot i need!!!

How well do u think uv dun? i fink i may hav gt a B

### #11loved-up-loon

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Posted 19 May 2006 - 03:12 PM

QUOTE(snowboardin_chik_5 @ May 19 2006, 04:10 PM)

I gt x= -2 and 2 as well
the max area was 128 and the min was 32
I thot the paper could hav been alot worse but im plezd with the exam. Hopefully iv gt wot i need!!!

Exactly what I got, x=2,-2 and max 128 and min 32!
Grrrrrr!!

### #12SncZ

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Posted 19 May 2006 - 04:00 PM

OMG so is that right or wrong , 2,-2 128 and 32 .... there has been so many different answers to it ?

i soooo hope im (were) right as then i will of got over 90% in eache paper

being fair im not that good at maths, just my teacher was amazing

### #13Hev

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Posted 19 May 2006 - 09:22 PM

the answer is 2 and 1 since -2 is off the graph

needless to say

i worked this out at home

i hate maths

paper 2 was such a slap in the face after paper 1

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Posted 19 May 2006 - 10:12 PM

greatest is A=32 and this occurs when x = 2
least is A= 20 and this occurs when x=1, x=4

### #15Hev

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Posted 19 May 2006 - 10:21 PM

i got that too, but i'm glad other people found it hard

i thought i was just dense lol

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