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Edexcel A2 C4 Mathematics June 2015 - Official Thread

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Original post by TeeEm
what time is the start time for C4 in your school?
13.00 / 13.15 or 13.30?


13.45 :/
13:45 here.
GUYS I Have a small question. In June 13. Q7 Why exactly is it that when the tangent to the curve is parallel to the y axis we equate the denominatior to zero and get y in terms of x and put it in the orig equation? like whats the logic behind that? :smile:

also what if it said parallel to the x axis? then what do we do?

please help me i will be eternally grateful :smile:
Original post by TeeEm
what time is the start time for C4 in your school?
13.00 / 13.15 or 13.30?


13:30
Original post by Gilo98
Any MS or model answers floating sob for this? Thanks


I did the C4 questions with my students yesterday but unfortunately I did not retain the answers because it was of no interest.

Tough related rates question ... I wonder who wrote it ...
Original post by kingaaran
Hopefully - that paper looks really nice, especially the vector question which is surprisingly easy.


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Are you referring to the triangle one?
How do you find the exact length of AB?
I got the square root of 61-60arccos(2/3) lol
Original post by Ripper Phoenix
GUYS I Have a small question. In June 13. Q7 Why exactly is it that when the tangent to the curve is parallel to the y axis we equate the denominatior to zero and get y in terms of x and put it in the orig equation? like whats the logic behind that? :smile:

also what if it said parallel to the x axis? then what do we do?

please help me i will be eternally grateful :smile:


dividing by zero produces infinite gradient
Original post by frozo123
Are you referring to the triangle one?
How do you find the exact length of AB?
I got the square root of 61-60arccos(2/3) lol


AB= square root of 21
Original post by TeeEm
I did the C4 questions with my students yesterday but unfortunately I did not retain the answers because it was of no interest.

Tough related rates question ... I wonder who wrote it ...


No worries,would you be able to check my answers?

Spoiler

Original post by ridirahman
AB= square root of 21


how did you do it?
Original post by Ripper Phoenix
GUYS I Have a small question. In June 13. Q7 Why exactly is it that when the tangent to the curve is parallel to the y axis we equate the denominatior to zero and get y in terms of x and put it in the orig equation? like whats the logic behind that? :smile:

also what if it said parallel to the x axis? then what do we do?

please help me i will be eternally grateful :smile:


If it's parallel to the y-axis, that means the tangent has no gradient - no rate of change of y with respect to x.

Once you have set the differential equal to zero, you have two unknowns and hence you need to use simultaneous equations to solve for those two unknowns. Since that tangent touches a point on that line, the equation you formed by equating your differential equal to zero must satisfy the equation of the line. Hence, you sub it in to work out the x and y.

With regards to your second question, I'm not too sure. If it's parallel to the x-axis, I don't think you can really have a gradient:

y2−y1x2−x1=y0 \frac{y2-y1}{x2-x1} = \frac{y}{0}.

You'd have a change of y, but the change in x will be 0, and you obviously can't divide by zero, so I think the gradient is undefined - someone will have to confirm that lol :-


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Original post by Maham88
13:30


Original post by IWantSomeMushu
13:45 here.


Original post by ridirahman
13.45 :/


Original post by kingaaran
13:15 or 13:30, depending on the invigilators and any 'issues' they have to face :tongue:


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Original post by Bustamove
I think the exam usually starts around 1PM.... if anything, maybe a few minutes late if your school is disorganised...


Original post by Naga7o
I start at 2, pretty late compared to other people


Original post by physicsmaths


thanks

it looks that it can be between 13.00 and 14.00 with 15 minute gaps
thanks to all...
I am off for my morning walk soon, then do some work, then prepare a C4 poll, then hear people cry ...
L1.jpg29.9KB
Original post by TeeEm
dividing by zero produces infinite gradient


okay and what if it said parallel to x axis?
Original post by frozo123
how did you do it?


c^2 = a^2 + b^2 - 2abcos (AOB)

then you subst. a and b like;

25 + 36 - 60(2/3) which gives you 21 so c^2 = 21 = square root of 21

hope this helps
(edited 8 years ago)
Original post by Ripper Phoenix
GUYS I Have a small question. In June 13. Q7 Why exactly is it that when the tangent to the curve is parallel to the y axis we equate the denominatior to zero and get y in terms of x and put it in the orig equation? like whats the logic behind that? :smile:

also what if it said parallel to the x axis? then what do we do?

please help me i will be eternally grateful :smile:


Ok so when the tangent is parallel to the Y- axis, it means the tangent is vertical and therefore has an 'infinite' gradient

The expression for dy/dx is -(2x+4y)/(4x+2y) for dy/dx = infinity the denominator must be equal to zero as anything divided by zero is undefined/infinite

so then you get 4x + 2y = 0 y = -2x substitute that into the original equation to solve and get the co-ordinates :biggrin:
Yep, before I head to school, any last key points to remember in the exam, anyone?
Original post by ridirahman
c^2 = a^2 + b^2 - 2abcos (AOB)

then you subst. a and b like;

25 + 36 - 60(2/3) which gives you 21 so c^2 = 21 = square root of 21


of right I was putting cos(2/3) in my calculator lol, thanks :smile:
Original post by Gilo98
No worries,would you be able to check my answers?

Spoiler



look at related rates book Q30
Original post by Ripper Phoenix
okay and what if it said parallel to x axis?


numerator zero.
Could someone please post the June 2015 C34 ial mark scheme please!

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