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semations

ok wel first they say express 2/(r+1)(r+3) in partial fractions
i did that the answer is 1/ r+1 - 1/(r+3)

then it says prove that the semation 2/(r+1)(r+3) = n(5n +13)/6(n+2)(n+3)

i tried it but i didnt get the right answer, if an yone can help thanx, its worth 5 marks.

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Which board?

Rose in Bloom

Which board?

edexcel

Reply 3

Rose in Bloom

Reason y I asked was I never heard of semations...enlighten me plz!...or I mightn't know because I did upto P3 only...which level is this?

Reply 4

S1M

kriztinae

summation...

is this p4?

i think ill give it a shot :smile:

Reply 5

kriztinae

Rose in Bloom

Reason y I asked was I never heard of semations...enlighten me plz!...or I mightn't know because I did upto P3 only...which level is this?

p4, paper 4 pure maths 4

Reply 6

kriztinae

S1M

summation...

is this p4?

i think ill give it a shot :smile:

thanx your a star!

Reply 7

Rose in Bloom

Ok sorry...can't help you, haven't done much.....apologies!
cheers :smile:

Reply 8

S1M

damn server error...

well i couldnt do it... but then i cheated (looked in markscheme) and now i can do it :smile:

what you need realise is that the 1/3 and the 1/(n+2) doesnt get cancelled so you are left with 5/6 - 1/(n+2) - 1/(n+3)
rather than typing it all out i have attached the mark scheme :biggrin:

if you wnat the rest of the markscheme; i can send it to your email :smile:

its too big to upload here :frown:

08_P4_January_2003_mark_scheme0.doc55.8KB

Reply 9

kikzen

i could do it.

you have your partial fractions and u start to add up the terms (1-->n).

the first two terms (on the left) dont cancel. and neither do the last two (on the right).

that is, 1/2 + 1/3 - 1/(n+2) - 1/(n+3)

which is 5/6 - 1/(n+2) - 1/(n+3)

which simplifies to what they give you

Reply 10

kriztinae

S1M

damn server error...

well i couldnt do it... but then i cheated (looked in markscheme) and now i can do it :smile:

what you need realise is that the 1/3 and the 1/(n+2) doesnt get cancelled so you are left with 5/6 - 1/(n+2) - 1/(n+3)
rather than typing it all out i have attached the mark scheme :biggrin:

if you wnat the rest of the markscheme; i can send it to your email :smile:

its too big to upload here :frown:

no i got the markscheme i still dont get it! show u how thik i am!
i got that far. dont worry, its just this one question i dont get, must be a silly mistake later!

Reply 11

S1M

kriztinae

no i got the markscheme i still dont get it! show u how thik i am!
i got that far. dont worry, its just this one question i dont get, must be a silly mistake later!

well kikzen has sort of explained it...
dont worry... your not thick... u got further than i did :frown:

u must have made a simple mistake in rearranging 1/2 + 1/3 - 1/(n+2) - 1/(n+3) into the required form...

Reply 12

kriztinae

yeah ok thanx! both of you thanx!
ill see what i can do :smile:

Reply 13

S1M

if your still having problems then i will type the rearrangement stuff out for ya... just let me know :smile:

Reply 14

kikzen

ill post a question here too actually.

there was a summation from 0 to n... how do you do that? i can do 1->n

found it!

solomon p4 paper e
2. show sum(r+1)(r+2) from 0 to n = 1/3(n+1)(n+2)(n+3)

:confused:

Reply 15

S1M

kikzen

wont it be the same as from r=1
but you just add 2 because when r=0, (r+1)(r+2)=2

Reply 16

Hope

I tried to do it for you, and started off the right way but then made a silly error too so I got it wrong - so don't worry about it!

S1M - do you live to serve? You help people an awful lot (not that anybody's complaining!) Do you not have exams yourself?