Edexcel FP1 Thread - 20th May, 2016

Original post by thelegend99

Basically means, prove that it's divisible by 3.

Yeah I know haha I was just unable to get the inductive step

Reply 828

AAls

15

When would I use/not use the proof method where u make f(k) = ()m ?

Reply 829

Original post by iMacJack

Yeah I know haha I was just unable to get the inductive step

Oh ok, have you got it now? I might give that one a try.

Reply 830

NotNotBatman

20

Original post by iMacJack

Any help with this proof by induction question please? Thanks!

@Zacken @NotNotBatman @kingaaran etc! Thank you!

Question from CM PBI worksheet

When doing the

f(k)-f(k+1)

, I find that's it's easier if you simplify the powers first, then when you subtract, group and rearrange, rather than having loads of brackets.

When you get to that stage 'force in' some multiple of

f(k)

, and then add/subtract to compensate and make it equal to your previous step. The multiple of

f(k)

should be so that the remaining bit is both divisible by 3.

If you look at the worked solutions to the divisibility test on madasmaths, this shows, imo, the best way to do it.

Reply 831

crashMATHS

Original post by iMacJack

Aha got ya.

Also, you know in the F1 Jan 16 paper you sit, you see the question about the coordinates of where the normal intersects the parabola again (or something along those lines) and you have a dirty quadratic with like p^3 and p^4's and what not - how on earth do you use the quadratic formula successfully to work out the coordinates?? I'm so baffled!

https://gyazo.com/98e0758d1498ec2a5addcd7bfc1f15ee

Part B is what I'm on about

I'd factorise. You already know that y=c/p (or x =cp) is a solution, so you know that one of the brackets must be (py-c). Then you can use inspection to see what the other bracket has to be :smile:

Reply 832

Original post by AAls

When would I use/not use the proof method where u make f(k) = ()m ?

proving something is divisible.

Reply 833

Original post by kingaaran

I'd factorise. You already know that y=c/p (or x =cp) is a solution, so you know that one of the brackets must be (py-c). Then you can use inspection to see what the other bracket has to be :smile:

Have you got the full paper with mark scheme?

Reply 834

AAls

15

Original post by thelegend99

proving something is divisible.

Yes, but does it always work or would I have to use a different method like f(k+1) -f(k)?

Reply 835

crashMATHS

Original post by thelegend99

Have you got the full paper with mark scheme?

I uploaded it. It got taken down. :/

Posted from TSR Mobile

Reply 836

Original post by AAls

Yes, but does it always work or would I have to use a different method like f(k+1) -f(k)?

I think that it would be better to use overall, but if you're comfortable with f(k+1) - f(k) method then use that. Don't change anything too late.

Reply 837

iMacJack