[ninuzu]

(Original post by crazymanny00)
if you have the FP1 book by OCR (Douglas quadling.. something) on page 30 there is an explanation on how this is done. It's a lengthy process but you get there...

Attachment 153037

Ah thanks, I get it now

[Maphs]

hey guys am i right in saying that for cubic roots...
1.alpha + beta + gamma = -b/a
2.(alpha x beta) + (alpha x gamma) + (beta x gamma) = c/a
3.Alpha x beta x gamma = -d/a

[crazymanny00]

thats right yeah

[Maphs]

If so than for january 2012 exam paper Q10)(ii) i substituted x = sqrt(u). and got the correct equation as shown in the mark scheme...
" 9u^3 - 45u^2 + 72u - 4 " this is definitely correct, the mark scheme says so, but how can c = -4/9 because " alpha x beta x gamma = -d/a, so should it not be just 4/9???

[crazymanny00]

i posted on that one earlier... i think it's because they started a on the x squarer coefficient not the x cubed and you had to use c/a not -d/a .... much confusion and trickery, but thats OCR for you

[Maphs]

look here is what the mark scheme says for it but i do not understand, they have done the same thing for a.

[Maphs]

EVEN " A " is done the weird way, but how comes if they started on the x squared one would the -45 now be the a??

[crazymanny00]

i just dont know...

[RooT_Fifteen]

So..... who's hoping for a hard paper....? :P

[crazymanny00]

you are right though, either were missing something or its wrong.... going more towards the ms being wrong haha

[crazymanny00]

(Original post by RooT_Fifteen)
So..... who's hoping for a hard paper....? :P

for lower grade boundaries? personally i don't think it will be too hard anyway

[88888]

LAST one to go , then halfterm!!!
anyone same???

[mathsman77]

(Original post by crazymanny00)
for lower grade boundaries? personally i don't think it will be too hard anyway

i'm not sure.. given ocr's other maths exams this year, i think my money is on it being a hard paper

[crazymanny00]

you could be right on that actually... S1 was hard.. i know M2 in jan was hard aswell but sitting that on the 22nd

[mathsman77]

I can tell you the D1 wasnt nice either (not that it ever is), and ah, good luck! this FP1 is my last exam 'till January

[mathsman77]

Can someone quickly run through part i?
I can't see how 13^n + 6^(n-1) + 13^(n+1) + 6^n = 14 x 13^(n) + 7 x 6^(n-1)

[As_Dust_Dances_]

Can someone please explain what you're meant to do when you're using method of differences then it asks for (sum of r=n+1 to infinity)?? Or if you have r=2 on the bottom of the sigma? I'm still confused.. :/

[Maphs]

hey guys, i was doing an induction question and i came to a point where, oh what the heck let me tell you the question.
The sum of ((2^r-1) = ((2^n) -1) from 1 to n
and i got to the stage of ((2^k)-1) + ((2^k+1) -1) where i inputted n = k + 1
and i do not understand how to simplify this to get = ((2^k+1) -1)
if you do not understand my writing could you just try and do the question yourself? if you understand the question?

[Dhanu123]

(Original post by As_Dust_Dances_)
Can someone please explain what you're meant to do when you're using method of differences then it asks for (sum of r=n+1 to infinity)?? Or if you have r=2 on the bottom of the sigma? I'm still confused.. :/

sum r=1 with n=infinity minus sum r=1 n=n i think

[Maphs]

hey guys, i was doing an induction question and i came to a point where, oh what the heck let me tell you the question.
The sum of ((2^r-1) = ((2^n) -1) from 1 to n
and i got to the stage of ((2^k)-1) + ((2^k+1) -1) where i inputted n = k + 1
and i do not understand how to simplify this to get = ((2^k+1) -1)
if you do not understand my writing could you just try and do the question yourself? if you understand the question?