Maths PP1

ZorbaTehZ

Crumbs wrote:

For the first part, did you get un = (2n-1)loge3 ?

That gives n < 18.5, so 18 terms.

Shít!
S(n+1) - S(n) = U(n) ...what I ****ing did.

At this rate Ill probably drop a grade...

Jonathan

Just while im here, on HL 7 c (ii)

Is saying that because you cannot x=0 in to the formula (as ln of 0 is undefined) prove that it never crosses the x axis?

JC 2K3

cocoa wrote:

rofl, I made almost the same mistake (only slightly less) I integrated from 1-5 when i should have integrated from 1-3... oh well

heh, I got 7, and since everyone else seemed to get 6 2/3, I've deducted that the little area I missed is 1/3 square units

I'm thinking they could take 10 marks for that blunder though, since I didn't subtract the two equations from each other, which I'm sure is worth 5.

genericgoon

Well at the x-axis y=o not x so no

cocoa

jmccrohan wrote:

Just while im here, on HL 7 c (ii)

Is saying that because you cannot x=0 in to the formula (as ln of 0 is undefined) prove that it never crosses the x axis?

no, that would be proving it doesn't touch the y-axis...

JC 2K3

ZorbaTehZ wrote:

At this rate Ill probably drop a grade...

Nah, you have to lose a whopping 60 marks between the two papers before you drop from an A1 to an A2.

genericgoon

XD A WHOLE 60 OMG! we all getting them As

Crumbs

cocoa wrote:

answers to ii and iii are incorrect:
(ii) 1, -k-2
(iii)k<-2

Indeed they are, thanks! I corrected them in my original post.

______

JC 2K3 wrote:

heh, I got 7, and since everyone else seemed to get 6 2/3, I've deducted that the little area I missed is 1/3 square units

I'm thinking they could take 10 marks for that blunder though, since I didn't subtract the two equations from each other, which I'm sure is worth 5.

I'm sure i'm grand, just work a bit for the paper 2 and i may be able to get an honour

CosaFada

what about saying loge3x -e^3x could not possibly equal zero is that true or just a random statement on my part!!:D

cocoa

CosaFada wrote:

what about saying loge3x -e^3x could not possibly equal zero is that true or just a random statement on my part!!:D

that's kindah what JC said (well, he said ln3x!=3x but anyway) but I don't really think it's so evident. Also, the word deduce kind of hints that you should use the first part. It might get you the marks, but it might not...

edit:

this is why the answer to 1(b)(iii) isn't k>-3 :
the formula b^2 -4ac>0 is for roots that are real, not positive!

genericgoon

I wrote down that ln thing but thought it was wrong so I just left it there and put down the thing about the second der. , always decreasing etc.

Crumbs

rjt wrote:

This is what I did, but afterwards began to think it wasn't rigorous - after all, this is just a local max point, not an absolute maximum for the function (eg. a cubic equation may have a local max, yet extend on to infinity). Would you not need to show that this is not the case with this function too? I'd love if this wasn't the case - it'd give me full marks on this question, but I'm skeptical.

True. I suppose we could show that for 0<x<1/3, f'(x)>0 and for x>1/3, f'(x)<0.
Therefore, the graph is always increasing up to the local maximum and then always decreasing afterwards.

cocoa

I just said this:
no other possible solution for f'(x)
therefore no other max/min point
therefore aforementioned point is absolute maximum
therefore line never goes higher than y=-1
therefore line never hits x-axis

ninebeanrows

Dammit, for Q7 b(i) i didnt do implicit diff i thought about it but then subbed in the points to the slope of the curve and said that was the slope of the line and put in the eqt of a line formula.

attempt marks!!?:o

cossyx

i faild d mock so considerin da i feel happy enough abou it! pity a theorem didn cum up bt at least d 1st principles did..hpefuly paper 2 wil b nice:D

T-b0n3

Tell me Im not the only one to be so foolish to get the slope of the tangent and not get the equation like asked..Did it in both of those questions.. Thats defo easy marks down the drain but found the paper very handy. Questions 1,2,3 especially.

Adam

cossyx

T-b0n3 wrote:

Tell me Im not the only one to be so foolish to get the slope of the tangent and not get the equation like asked..Did it in both of those questions.. Thats defo easy marks down the drain but found the paper very handy. Questions 1,2,3 especially.

Adam

nope ur not i did too...nly realised after!! so annoyin..bt nothin cn b dun nw!:o

T-b0n3

Yea I know wouldnt mind if I didnt know how to do it or something but like seriously come on its just such a waste :(:mad: :mad:

qwertykeyboards

was question 6 c (ii) a misprint?? accordin to one of my mates in another school it was a misprint and everyone will get the 20 marks for it! hope so! was meant to be f '(x) not f (x).

cocoa

no, f(x) was correct... there's a total answer typed out somewhere in this thread...

ashyle

ooh that would be nice. i suck at that question.

I thought it was a piece of cake in general.(OL) did all the questions cos I HAD SO MUH SPARE TIME!! It's way too long innit??? Loved q.1. so simple. loved the series and sequences too, somehow remembered the formulae

qwertykeyboards

im talkin higher level now but yeah prob is right wrecked me head tho!

T-b0n3

No it wasnt a misprint but fourtunetly for me i mis read it and thought it said g(x)+f(x) and added them together and got zero only to realised i had misread it and I then put a line through it. So im sure ill end up getting the marks by accident as it happens but doesnt bother me which way I get marks!!..

Adam

mathew

for question 7 part with proving it didnt cut the axis i just got the horrizontal asymptot. Basicly the limit of f'(x) as x -> infinity.. gave me y=0 which means that the x axis is an asymptot, so the curve approaches it but never touches it...

T-b0n3

I got that the x-aixs is an asmytop too but dont think i did it right. Hopefully I did anyway.

Tomlowe

yeah i think mathews got it probably, i tried that but failed, got f''(x) is always negative, but i dont think thats enough.... hope ill get some marks anyway

qwertykeyboards

what did everyone get for higher level question 3 c (ii)

i got some mad + or - square root of some bollix!

mathew

qwertykeyboards wrote:

what did everyone get for higher level question 3 c (ii)

as far as i remember it was (4+i)... it said find the two complex numbers but they were both the same!!.. hence the square i suppose!

T-b0n3

Was plus or minis (4 + i) if i remember right..