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D1 finding cuts

http://math.mdsalih.com/Data/Edexcel%20Mathematics/D1/D1%20Jun%2003.pdf

Question 7)c) How did they get their C2 value? In the mark scheme it's like 81 but I got 93.... Aitch I need you!
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ljfrugn
http://math.mdsalih.com/Data/Edexcel%20Mathematics/D1/D1%20Jun%2003.pdf

Question 7)c) How did they get their C2 value? In the mark scheme it's like 81 but I got 93.... Aitch I need you!


you don't count EF or DG because they go right to left.
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username22878
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I don't understand why they're going right to left, it looks like theyre going left to right to me...
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ljfrugn
I don't understand why they're going right to left, it looks like theyre going left to right to me...


Extend the dotted line C2 up and down, and get quite clear about which side each vertex lies on...

D E H T1 T2 are right, all of the others are left, of the C2 line.

now E is right and F is left, so E->F is right to left so don't count it...
... and D is right and G is left, so D->G is right to left so don't count it...

Aitch
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username22878
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Oh, I see. Thanks.
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ljfrugn
Oh, I see. Thanks.


This is easy to miss under exam pressure. There are a couple of recent threads in which the "right to left" arcs, which have to be ignored, are an issue. It might be worth your while trawling back through the threads of the last couple of weeks to find them.

Aitch

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