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Edexcel A2 C4 Mathematics June 2015 - Official Thread

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Original post by physicsmaths
Should be right angle at L2. You can work this out differentiation or completing the square which would work all the time.


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Opposite to B? How did you know the right angle would be there?!?!
EDIT: nvm got it!!! those are the kind of ridiculous mistakes i make :/
(edited 8 years ago)
I hate c3 trignometry

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Original post by cerlohee
Thanks!! Your handwritings rly difficult to read haha. What does it say after "differentiate to"?


Differentiate to kinimise inside of square root lol.


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Original post by physicsmaths
Differentiate to kinimise inside of square root lol.


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Can't you just expand and solve? (having squared both sides to remove the root)

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Original post by powelsmartin
Can't you just expand and solve? (having squared both sides to remove the root)

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No, as there nothing to square and expand. We need to find the minimum value of that expression. Hence easily minimis the inside and since it is a quadratic we know its a minimum is for f'(y)=0 hence using chain rule as expanding it is just very long and error prone!


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Original post by cerlohee
Opposite to B? How did you know the right angle would be there?!?!
EDIT: nvm got it!!! those are the kind of ridiculous mistakes i make :/


How did I know? I can see the matrix.


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I can't do vectors in C4 at all, or M1 they are so hard
Original post by physicsmaths
No, as there nothing to square and expand. We need to find the minimum value of that expression. Hence easily minimis the inside and since it is a quadratic we know its a minimum is for f'(y)=0 hence using chain rule as expanding it is just very long and error prone!


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Right, I thought you set it equal to the length since that's what's usually done :smile:

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Original post by powelsmartin
Right, I thought you set it equal to the length since that's what's usually done :smile:

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It is the length but it is unknown so set it as a function of lambda


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Original post by physicsmaths
It is the length but it is unknown so set it as a function of lambda


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Yeah I got that but there must be another way of solving it - trig if you know the angle and the other two sides since you usually find those in previous parts of the question? I just don't remember ever needing to use differentiation in vectors and I've done every paper since 2010.

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Original post by physicsmaths
It is the length but it is unknown so set it as a function of lambda


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Hmm. Is there a specific place you learned this? As I can't understand the principles of what's going on, but I understand what you've done, just not why you did it.
Reply 511
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Tplox
2
Anyone know where I can find loads of vectors questions?


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Original post by dominicwild
Hmm. Is there a specific place you learned this? As I can't understand the principles of what's going on, but I understand what you've done, just not why you did it.


Duno just figured it out tbh. It felt like a natural thing for me to do.


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Reply 513
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TeeEm
19
Original post by Tplox
Anyone know where I can find loads of vectors questions?


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Look at the links in post 58 of this thread

http://www.thestudentroom.co.uk/showthread.php?t=3327325
Reply 514
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TeeEm
19
Original post by SOREN_TORETTO
I hate c3 trignometry

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trigonometry is beautifully amazing ...
How are people planning on revising for the newer/harder style papers we seem to be getting?

I feel like if this years C1 and C2 papers have been hard C3 and C4 will be even harder :redface:
Original post by Saywhatyoumean
How are people planning on revising for the newer/harder style papers we seem to be getting?

I feel like if this years C1 and C2 papers have been hard C3 and C4 will be even harder :redface:


My teacher gave me a set of about 100 tough exam questions from a variety of boards. Seems as good practice as any.

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Original post by Krollo
My teacher gave me a set of about 100 tough exam questions from a variety of boards. Seems as good practice as any.

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I wish my teacher did that tbh, are they online or sheets?


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Original post by Saywhatyoumean
I wish my teacher did that tbh, are they online or sheets?


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Sheets, I could post them here if you wanted?

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Original post by Krollo
Sheets, I could post them here if you wanted?

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Yes please! Do they have answers too??


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