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Edexcel FP2 June 2015 - Official Thread

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Reply 140

jf1994

Does anyone know why the S13 FP2 paper was withdrawn?

Reply 141

username1162972

Original post by 1 8 13 20 42

No; they may seem to enjoy challenging people lately but I don't think they're allowed to ask that

Assuming true for positive integers. Let n=-m where m<0
The proof follows.

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Reply 142

tggfootymad

Original post by 1 8 13 20 42

No; they may seem to enjoy challenging people lately but I don't think they're allowed to ask that

I know, S3 didn't go at all as planned....but I think asking for a proof by induction for negative integers goes beyond what they could reasonably ask. Let's hope...!

Reply 143

tggfootymad

Original post by physicsmaths

Assuming true for positive integers. Let n=-m where m<0
The proof follows.

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But how do you do it in terms of proof by induction? With K, K+1 etc, as how would that work with a negative integer proof for de moire?

Reply 144

math42

Original post by physicsmaths

Assuming true for positive integers. Let n=-m where m<0
The proof follows.

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I know a proof follows from that; I was saying that they wouldn't ask us to do it with induction

Reply 145

Maths degree

can somebody help me out as to why in june 09 q 6b they shade the outside region of the circle rather than inside esp as they stated its less than 3 :s

Reply 146

math42

Original post by Maths degree

can somebody help me out as to why in june 09 q 6b they shade the outside region of the circle rather than inside esp as they stated its less than 3 :s

The locus of z was z < |3|, you're sketching the locus of w
If you go back through your workings to find the locus of w, imagine a less than sign instead of an equals sign (look carefully to see if it will have swapped at any point) and you'll find the inequality for w

Reply 147

phawkins96

I'm just hoping we won't need to sketch a polar curve..

Reply 148

Mjmuk

I just have a couple questions:1. Do we need to know how to prove things like the integrating factor etc. or is it just De Moivres that we'll be expected to prove in the exam?2. In Exercise 3E Q7a When they are solving it they add the 2k(pi) AFTER they multiply the equation by 4 using De Moivres, and I tried to solve it by adding 2kpi before the multiplication but got different answers. So when we get a question like this do we only add 2kpi after multiplying and before ''dividing (by 3 in this case)'' and why does it make a difference?3.In Example 31 in Complex Numbers Pg 48 , For finding Min/Max values does the line ALWAYS have to pass through the centre of the circle regardless of where it starts ie max from z-1 4. And finally how do you draw arg(1-w)=pi/2 ?Thanks in advance

Reply 149

username1162972

Original post by Mjmuk

arg(1-w) is a half line going down. Hint tan is odd fucntion so arg(w-1)=-pi/2

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Reply 150

Anshul6974

Original post by physicsmaths

arg(1-w) is a half line going down. Hint tan is odd fucntion so arg(w-1)=-pi/2

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Can you explain why arg(1-w)=pi/2 is the same as arg(w-1)=-pi/2?
Thanks

Reply 151

Boop.

Original post by Anshul6974

Can you explain why arg(1-w)=pi/2 is the same as arg(w-1)=-pi/2?
Thanks

arg(1-w) = pi/2
=> arg[-1(w-1)] = pi/2
arg(-1) + arg(w-1) = pi/2
pi + arg(w-1) = pi/2
therefore: arg(w-1) =pi/2 - pi
arg(w-1) = -pi/2

(edited 8 years ago)

Reply 152

Mjmuk

Original post by Boop.

arg(1-w) = pi/2
=> arg[-1(w-1)] = pi/2
arg(-1) + arg(w-1) = pi/2
pi + arg(w-1) = pi/2
therefore: arg(w-1) =pi/2 - pi
arg(w-1) = -pi/2

Thank you, this makes a lot more sense!

Reply 153

kprime2

For the proof by induction of De Moivre, is it acceptable to prove it generally for k? What I mean is can we not just use the letter k then say somewhere at the top that (k<0)? Or do they want us to use the negative sign i.e. when n=-k, then when n = (-k-1) etc?