Edexcel C4 June 2014- OFFICIAL THREAD

If a graphnis rotated through pi radians rather than 2 pi radiands do we caluslate pi/2 multiplied bycthe integral of y^2dx as the graph is only rotated half way?

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Reply 981

mb07

Good luck everyone! Hope everyone gets the marks they lost on C3 :biggrin:

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Reply 982

Jaydude

11

Original post by stephen95

how do you integrate 1/sin^2(2x)

Turn that into cosec^2(2x), then I'm guessing you can do it from there, if not just quote me again.

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Reply 983

stephen95

Original post by Jaydude

Turn that into cosec^2(2x), then I'm guessing you can do it from there, if not just quote me again.

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Thanks just realised myself how to do it haha

Reply 984

Mutleybm1996

19

Original post by IWantSomeMushu

Thanks

Cosec^2 x ->>> -cotx

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Reply 985

Mutleybm1996

19

Original post by Jaydude

Turn that into cosec^2(2x), then I'm guessing you can do it from there, if not just quote me again.

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Is it 1/2 cot 2x?

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Reply 986

dogs4eva7

20

http://examsolutions.net/a-level-maths-papers/worked-solution/worked-solution.php?paper_id=408&solution=7.2

When he says 'tangent is parallel to y-axis when denominator = 0', why is that?
Why does the denominator have to be 0?

Reply 987

mo_masquerade

2

Original post by jenigma

http://examsolutions.net/a-level-maths-papers/worked-solution/worked-solution.php?paper_id=408&solution=7.2

When he says 'tangent is parallel to y-axis when denominator = 0', why is that?
Why does the denominator have to be 0?

Gradient goes to infinity and this only happens in a fraction when the denominator is equal to 0.

Reply 988

Pascal678

Original post by jenigma

http://examsolutions.net/a-level-maths-papers/worked-solution/worked-solution.php?paper_id=408&solution=7.2

When he says 'tangent is parallel to y-axis when denominator = 0', why is that?
Why does the denominator have to be 0?

A tangent parallel to the y-axis is basically a straight line i.e. the same x-coordinate throughout the tangent

So the change in x with respect to the change in y is in fact 0

This means

\dfrac{dx}{dy}=0

(edited 9 years ago)

Reply 989

Cerdic

18

Original post by Nick214

I thought a fraction when it's doninator was 0 was undefined or something?

Well yeah, it's not great maths to say that a fraction is infinite which is why it's better to think of it in terms of dx/dy, but you can see that as the denominator tends to zero ceteris paribus, the fraction tends to infinity.

Reply 990

DaveJHH

Who else has to take this exam earlier than 1:00 :frown:

Reply 991

dogs4eva7

20

Original post by Pascal678

A tangent parallel to the y-axis is basically a straight line i.e. the same x-coordinate throughout the tangent

So the change in x with respect to the change in y is in fact 0

This means

\dfrac{dx}{dy}=0

Original post by mo_masquerade

Gradient goes to infinity and this only happens in a fraction when the denominator is equal to 0.

Thank you for your speedy replies! (':

So when the question states that x is negative and that the tangent is parallel to the y-axis, is that just another way of saying 'find the coordinates when dy/dx = 0'? (like in the other papers)

Reply 992

Pascal678

Original post by jenigma

Thank you for your speedy replies! (':

So when the question states that x is negative and that the tangent is parallel to the y-axis, is that just another way of saying 'find the coordinates when dy/dx = 0'? (like in the other papers)

No its a bit different this time. If it was a tangent parallel to the x-axis then

\dfrac{dy}{dx}=0

(a diagram always helps) Think about a tangent like y=3, as the y doesn't change as x varies so the gradient is 0

If a tangent is parallel to the y-axis then

\dfrac{dx}{dy}=0

x-coordinate is negative means ignore x-coordinates you retrieve that are greater or equal to 0

(edited 9 years ago)

Reply 993

Karoel

6

Original post by sarchi

were you referring to this question? because the substitution makes it soooo much easier to solve then :/

What is the answer? I got

\frac{1}{6\ln 2}

Reply 994

sarchi

Original post by Tplox

can someone post a pic of jan 14 the last question about vectors
i dont know how to do the last 2 parts

This is the whole question, hope it helps and i continued part f on the top, i've indicated with a star (kinda)

jan 2014.jpg

Reply 995

itssimplyme

14

Think I'm going to call it a day now!

Good luck tomorrow - don't forget to check check check! Can't afford to lose those UMS :teehee:

Reply 996

stephen95

can someone help me with part B on this question just on how to find out what x value to use

c4.png34.6KB

Reply 997

Pascal678

Original post by Karoel

What is the answer? I got

\frac{1}{6\ln 2}

That is correct

Reply 998

Dilzo999

19

Tips on connected rates of change:
Look out for keywords, when it's like something pouring out, look to see whether it says increase or decrease. A decrease means you just stick a negative in front. Also check to see other hints e.g. cm^3, change in time, rate at which, these are the main ones, after you've formed your DE the question becomes extremely simple afterwards.

Reply 999

StoneSour0135

3

Do we need to know how to integrate something like 2^x?

Edexcel C4 June 2014- OFFICIAL THREAD

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