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# Edexcel A2 C4 Mathematics June 2016 - Official Thread watch

1. (Original post by lordoftheties)
Would the value of the constant ( ' +C ' ) when doing a differential equation change? Im inclined to think that because its the 'constant' it doesn't change even if the x and y values do change...
Well yes, it doesn't change. Constant is dependent on the initial conditions. In a first order equation e.g. dx/dt = f(t) you will need one initial condition, for instance x(0) (i.e. the value of x at t = 0) and then you can decide the constant. If no specific conditions are given you put it there to account for arbitrary initial conditions.
2. Any predictions for the harder questions this year? The ones you see in questions 7c or 8d, you get the gist
3. If I want to get an A*, do I only need an average 90% in C3 and C4, as long as my score in M1 adds up to an overall 80% of the entire A level maths?
4. (Original post by QueenOfNachos)
If I want to get an A*, do I only need an average 90% in C3 and C4, as long as my score in M1 adds up to an overall 80% of the entire A level maths?
480+ UMS overall with 180+ UMS from C3 and C4 combined.
5. can someone please explain to me how to integrate by reverse substitution im honestly awful at this part
6. (Original post by Kavitaa.xo)
can someone please explain to me how to integrate by reverse substitution im honestly awful at this part
find an example question for us to work through
7. Q) If a question provides a function f(x) and asks you to work out the range .... I normally would put the limit of the domains into f(x) find a value and try to sketch a graph. I did that for a question in a past paper but only scored 1/3 marks (-2 marks loss) due to not realising that you have to complete the square of the function f(x) and then use the max value of the domain into f(x) so say min value = -2.25 via complete square and max value = 10 .*. say -2.25<= f(x) <= 10

Do you always have to complete the square if the question provides a function f(x) and asks to find the range? It did seem a bit fishy due to the question being worth 3 marks.
8. (Original post by XxKingSniprxX)
Q) If a question provides a function f(x) and asks you to work out the range .... I normally would put the limit of the domains into f(x) find a value and try to sketch a graph. I did that for a question in a past paper but only scored 1/3 marks (-2 marks loss) due to not realising that you have to complete the square of the function f(x) and then use the max value of the domain into f(x) so say min value = -2.25 via complete square and max value = 10 .*. say -2.25<= f(x) <= 10

Do you always have to complete the square if the question provides a function f(x) and asks to find the range? It did seem a bit fishy due to the question being worth 3 marks.
Well if it was a trig function of power 1 you won't be able to complete the square.
Ranges occur such that they are at the end points of increasing and decreasing intervals. Hence at these endpoints min and max occur for such domains. You need to use these facts, rewriting some functions does help massively.

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9. Help with very hard/confusing Differentiation question! @Q10 (b)

To prove that via differentiation seems ever so hard/challenging and I tried looking at the mark scheme but they look even more confusing!

I saw alternative way to proving it is to realise integration is the reverse of differentiation so if you prove the right side can be integrated to give the left side than its fine. I saw on the mark scheme that if you quote just the integral from the formula sheet you instantly get 4/4 marks. is this hippy sh1t.... So much work involved differentiating whereas just using the formula sheet is bam less than 20 seconds = 4/4.

How often do you have to use reverse differentiation? I've only seen it once (now) after 9 past papers.

Right click and open the image in a new tab and zoom in. sorry

Spoiler:
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sorry for the huge space gap blame paint
10. (Original post by XxKingSniprxX)
...
Could also just notice that
11. (Original post by XxKingSniprxX)

To prove that via differentiation seems ever so hard/challenging and I tried looking at the mark scheme but they look even more confusing!

How often do you have to use reverse differentiation? I've only seen it once (now) after 9 past papers.
Spoiler:
Show
sorry for the huge space gap blame paint
What's hard in differentiating that? It's just using chain rule:
Spoiler:
Show

Maybe perhaps you're having trouble applying the chain rule here?
Spoiler:
Show

You see, I can basically skip all these steps and literally do them in my mind after being quite familiar with the Chain rule.

Reverse differentiation, is a basic concept and also the same thing is done when Reverse chain rule is used / Integration by Recognition etc.
12. (Original post by XxKingSniprxX)
Q) If a question provides a function f(x) and asks you to work out the range .... I normally would put the limit of the domains into f(x) find a value and try to sketch a graph. I did that for a question in a past paper but only scored 1/3 marks (-2 marks loss) due to not realising that you have to complete the square of the function f(x) and then use the max value of the domain into f(x) so say min value = -2.25 via complete square and max value = 10 .*. say -2.25<= f(x) <= 10

Do you always have to complete the square if the question provides a function f(x) and asks to find the range? It did seem a bit fishy due to the question being worth 3 marks.
This kinda question needs a bit of thought on what kind of graph you're dealing with, and as you said the domain provided. So say you were given a linear graph, you'd simply put in the domain and lay it out as an inequality. For a quadratic, as you said, you would calculate the minimum/maximum through differentiation/completing the square. As for trig graphs, you know that a sin and cos graphs have a maximum at 1 and a minimum at -1. Then you can apply any transformation/translations that the given function has undergone to get your maximum and minimum value for the range.
What's hard in differentiating that? It's just using chain rule:
Spoiler:
Show

Maybe perhaps you're having trouble applying the chain rule here?
Spoiler:
Show

You see, I can basically skip all these steps and literally do them in my mind after being quite familiar with the Chain rule.

Reverse differentiation, is a basic concept and also the same thing is done when Reverse chain rule is used / Integration by Recognition etc.
Thanks a lot I understood it once I saw your method + latex =
Sucks not being able to write in latex got to resort so such a long route.

I am familiar with chain rule etc just either went blank/gave up when I got half way to the answer.
14. (Original post by XxKingSniprxX)
Thanks a lot I understood it once I saw your method + latex =
Sucks not being able to write in latex got to resort so such a long route.

I am familiar with chain rule etc just either went blank/gave up when I got half way to the answer.

if you're quite unsure, It's a good idea to resort to writing everything down, from your basic concepts (Make sure you polish them well!).

Better be correct with a bit more effort rather than have the answer wrong.
15. For c4 has everything been asked from the spec? Last year you had to integrate a^x and that's never come up before.

Thanks

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What's hard in differentiating that? It's just using chain rule:
Spoiler:
Show

If you could help me out, what exactly does it mean when they put d/dx in the question? because I ended up trying to form a differential equation (seems stupid now.) As in, why didn't they just say: prove ln(tan0.5x)=cosecx. Does it mean that ln(tan0.5x) has to be differentiated?
17. (Original post by Dohaeris)
As in, why didn't they just say: prove ln(tan0.5x)=cosecx.
Because you can't prove that, mainly because it's not true.
18. (Original post by Zacken)
Because you can't prove that, mainly because it's not true.
Yeah, after looking it up online, I think I get it now. So the d/dx means the derivative of ln(tan0.5x), so d/dx ln(tan0.5x)=cosecx means that differentiating ln(tan0.5x) should give cosecx?
19. (Original post by Dohaeris)
Yeah, after looking it up online, I think I get it now. So the d/dx means the derivative of ln(tan0.5x), so d/dx ln(tan0.5x)=cosecx means that differentiating ln(tan0.5x) should give cosecx?
Yeah, d/dx(f(x)) is notation for differentiating the function f(x).
20. (Original post by imran_)
For c4 has everything been asked from the spec? Last year you had to integrate a^x and that's never come up before.

Thanks

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