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# C2 Proof watch

1. How to prove the sum of a geometric sequence

i got this so far

what to do next?
Spoiler:
Show
Of course i've proved it i just want someone to show me why they do each step instead of me brainlessly proving it without understand doing it xD
2. (Original post by thefatone)
How to prove the sum of a geometric sequence

i got this so far

what to do next?
Spoiler:
Show
Of course i've proved it i just want someone to show me why they do each step instead of me brainlessly proving it without understand doing it xD
Subtract the two so that most of the terms cancel out.
3. (Original post by Zacken)
Subtract the two so that most of the terms cancel out.
ok
lets call rSn 2 and Sn 1
1-2
???
4. (Original post by thefatone)
ok
lets call rSn 2 and Sn 1
1-2
???
No. Try again, what does subtraction mean? Do you understand the difference between subtraction and addition? How did you get ?
5. (Original post by Zacken)
No. Try again, what does subtraction mean? Do you understand the difference between subtraction and addition? How did you get ?
To me

right i see so it must be thanks for clearing that up
6. (Original post by thefatone)
To me

right i see so it must be thanks for clearing that up
Yep.
7. (Original post by Zacken)
Yep.
phew that was close almost asked for help on the integration question(8) then realised i made a mistake on the first bit
where i said

the gradient of the normal is

when i said earlier on

at least i didn't get it wrong and the last question was a show ^-^ what a lifesaver "show" is....
8. (Original post by thefatone)
phew that was close almost asked for help on the integration question(8) then realised i made a mistake on the first bit
where i said

the gradient of the normal is

when i said earlier on

at least i didn't get it wrong and the last question was a show ^-^ what a lifesaver "show" is....
Good going.
9. (Original post by Zacken)
Good going.
phew hopefully 100% in this paper ....

hope
10. Good job.
11. (Original post by Zacken)
Good job.
https://b940eb267c31463d4d23ccfd3105...%20Edexcel.pdf
question 3

where do they get the y value of 3 from????
12. (Original post by thefatone)
https://b940eb267c31463d4d23ccfd3105...%20Edexcel.pdf
question 3

where do they get the y value of 3 from????
Uhm... you have the equation y = x + 4/x^2 that gives you the y coordinate for every x coordinate you plug in...
13. (Original post by Zacken)
Uhm... you have the equation y = x + 4/x^2 that gives you the y coordinate for every x coordinate you plug in...
yes so i got 2 as an x-cood oh poop....
lost another mark there *cries

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