# OCR (not MEI) Core 3 - 19/01/2011Watch

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8 years ago
#221
(Original post by ElMoro)
I didn't say it was wrong.

I was just showing them that 12*pi*ln(25)=24*pi*ln(5)
I know, but you should ALWAYS check equivalent values on a calculator; tip
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8 years ago
#222
(Original post by trix909)
What did people actually get for the first question?

For reference the first question was: |3x + 4a| = 5a, where a is a positive constant.

I just did +- (3x+4a) =5a, and got 3x = a and -1/3x= a
This is the correct answer (assuming you typed the question right, I didn't take the exam). However, I would imagine you would have to give x in terms of a, ie. right

x = a/3 and x = -3a as a would probably be the constant and x is the variable. However, this would not lose you many marks.
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8 years ago
#223
(Original post by Mr M)
Ok, I have just been sent a paper so will sort some answers out now. See you in half an hour!

haha I wish I could to this in half an hour
1
#224
(Original post by Mr M)
Ok, I have just been sent a paper so will sort some answers out now. See you in half an hour!
Who has sen you the paper? So I can rep them aswell
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8 years ago
#225
Question, and probably a stupid one at that. Everyone seems to have put that it was f(x) that had an inverse. I, being an idiot, forgot about e^x being the inverse of Lnx, so I worked out the inverse of g(x) instead. Thing is, it seemed to work. Anyone care to explain to me why that's not a valid inverse?
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#226
(Original post by houseelf)
Question, and probably a stupid one at that. Everyone seems to have put that it was f(x) that had an inverse. I, being an idiot, forgot about e^x being the inverse of Lnx, so I worked out the inverse of g(x) instead. Thing is, it seemed to work. Anyone care to explain to me why that's not a valid inverse?
g(x) had an x^2 in it so it isn't a one-to-one function there is no inverse.

Like if you have x^2=4 you don't know if x=2 or x=-2.
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8 years ago
#227
(Original post by houseelf)
Question, and probably a stupid one at that. Everyone seems to have put that it was f(x) that had an inverse. I, being an idiot, forgot about e^x being the inverse of Lnx, so I worked out the inverse of g(x) instead. Thing is, it seemed to work. Anyone care to explain to me why that's not a valid inverse?
It's not valid as g(X) was a many-to-one function so the inverse would be a one to many equation and so wouldn't be a function.
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8 years ago
#228
(Original post by ElMoro)
g(x) had an x^2 in it so it isn't a one-to-one function there is no inverse.

Like if you have x^2=4 you don't know if x=2 or x=-2.
Aha. Totally didn't think about that. Damn, that's another 3 marks thrown away.
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8 years ago
#229
balls! i forgot to write pi in the volume of revolution thing =[ (i always do that)
but all the answers ive seen here look familiar so otherwise im feeling good
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8 years ago
#230
(Original post by houseelf)
Question, and probably a stupid one at that. Everyone seems to have put that it was f(x) that had an inverse. I, being an idiot, forgot about e^x being the inverse of Lnx, so I worked out the inverse of g(x) instead. Thing is, it seemed to work. Anyone care to explain to me why that's not a valid inverse?
It Was Not A One-One Function

Needs To Be One-One To Define Its Inverse
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8 years ago
#231
0
8 years ago
#232
(Original post by ElMoro)
Who has sen you the paper? So I can rep them aswell
stowler91 - http://www.thestudentroom.co.uk/member.php?u=619132

(Thanks for the paper, how did you get it btw? )

P.S Shocking paper, I'll get 45/72 if Im generous :/
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8 years ago
#233
(Original post by Oh my Ms. Coffey)
I got that.

I divided the two rates.
I'm afraid I was actually doing the MEI C3 exam so you'll have to ignore what I said...
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8 years ago
#234
who did question 6i? i could not work out what dy/dx simplified to! i got

is this right? how would you simplify it?

edit: also, how many marks would i get for this working? the question is out of 4
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8 years ago
#235
(Original post by Princess_perfect786)
who did question 6i? i could not work out what dy/dx simplified to! i got

is this right? how would you simplify it?
Make it equal zero so therefore you can get rid of the denominator. Then multiply out the brackets and then rearrange
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8 years ago
#236
(Original post by *Lucy)
Mr M is a member of TSR whose profession/job is a Mathematics teacher so he got access to the paper, attempted it in his own time (not usually more than 20 minutes ) and then puts the answers up.

Being a teacher, respected member and frequent face in the Mathematics forums, his answers are trusted and appreciated
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8 years ago
#237
(Original post by godexists1234)
balls! i forgot to write pi in the volume of revolution thing =[ (i always do that)
but all the answers ive seen here look familiar so otherwise im feeling good
You should get all the marks, minus 1.

So if the question was worth 9, you should get a respectable 8
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8 years ago
#238
(Original post by nomzie)
LOL WAT DOES EVERY THINK IS A JUSTIFIED OR LIKELY GRADE BOUNDARY FOR THIS EXAM?

personally i think an A could be 45/72
I reckon it will be more like 48-50
Everyone said they found it hard but looks like theyve all got the right answers unlike me :\

Just looked at the answers and i would give myself about 46/ 72 and i was being generous!
Bloody brilliant, needed an A as well

Hello retake!
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8 years ago
#239
i think the grade baoundary for an A will be 54 max, any1 think anythink?
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8 years ago
#240
Made a right mess up of that exam. Need an A* for my uni offer as well so looks like a resit is in order. Hopefully they'll lower the boundaries though :/

Got the Cot(o) = 4 question entirely wrong, and the very last Q, last part I made a stupid error (forgot to sub the x-value back in to get the range). Also think I've got one of the G(x) F(X) questions wrong, the one where it was differentiate (lnX)^2 + 8 or something... I put 2lnX like an idiot...

So yeah, I'd guess that's what, 12 marks lost :/? Definitely no A* for me D:
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