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# C3 Help?? Watch

1. Taking the exam in January, anybody got any advice for how to revise most effectively? i.e. past papers or questions from the textbook?

x=(some function of)y [for example x=2siny]

How would you deal with that? I missed the whole chapter on functions when they covered it before summer, and my teacher has been very hasty with just completing the book. (I've caught up to some extent, but there are some things I don't fully grasp). Any help will be much appreciated!
2. Past papers FTW
3. (Original post by JH-QC)
Taking the exam in January, anybody got any advice for how to revise most effectively? i.e. past papers or questions from the textbook?

x=(some function of)y [for example x=2siny]

How would you deal with that? I missed the whole chapter on functions when they covered it before summer, and my teacher has been very hasty with just completing the book. (I've caught up to some extent, but there are some things I don't fully grasp). Any help will be much appreciated!
Which exam board are you with and, more specifically, which part of functions are you stuck (e.g Domain and Range, Finding the Inverse, Composite Functions etc) and is there any other topic you would like assistance on?

If you dont know anything about functions, it is really important to start reading now! It can take time to click.
4. (Original post by M1K3)
Which exam board are you with and, more specifically, which part of functions are you stuck (e.g Domain and Range, Finding the Inverse, Composite Functions etc) and is there any other topic you would like assistance on?

If you dont know anything about functions, it is really important to start reading now! It can take time to click.
Thank you for the response, it's Edexcel. I can do the inverse and composite functions questions from the textbook, but I can't find a question in there where an equation is set out in the aforementioned way (e.g. x=2siny) but I was doing a past paper and that came up. I'm assuming that's the inverse of something, but I wouldn't know how you deal with it
5. Ahh, firstly sorry for the late reply, so precisely what was this past paper question involving x=2siny?
6. (Original post by JH-QC)
Thank you for the response, it's Edexcel. I can do the inverse and composite functions questions from the textbook, but I can't find a question in there where an equation is set out in the aforementioned way (e.g. x=2siny) but I was doing a past paper and that came up. I'm assuming that's the inverse of something, but I wouldn't know how you deal with it
There should be values for x or y, if not, there must be a way to deduce it from the question paper, which year and question number is it?
7. Assuming you need to express y in terms of x
x=2siny
siny=x/2
y=arcsin(x/2)
now draw a right angled triangle with an angle labelled y. You know from the equation that sin y is x/2, so the hypotenuse is 2 and the opposite is x. You can work out the adjacent by pythagorus, you should get (4-x^2)^(1/2). I'm don't know what question you're referring too but generally they'll ask you to find cos(y) or something similar in which case you can use the triangle you have drawn.
8. The paper is Edexcel 18th Jan 2007, Q3

It says:

The curve C has equation x=2siny
(a) show that the point P (?2,?/4) lies on C
(b) show that dy/dx=1/?2 at P

Edit: Symbols didn't work -- point P co-ordinates are Square Root of 2, Pi over 4; and dy/dx is 1/root 2
9. (Original post by JH-QC)
The paper is Edexcel 18th Jan 2007, Q3

It says:

The curve C has equation x=2siny
(a) show that the point P (?2,?/4) lies on C
(b) show that dy/dx=1/?2 at P

Edit: Symbols didn't work -- point P co-ordinates are Square Root of 2, Pi over 4; and dy/dx is 1/root 2
For a) If you sub in the y coordinate you're given, it should give out root 2.

For b) Find y in terms of x, differentiate and sub in x = root 2.

If you can't see why you'd do either of those then please ask!
10. (Original post by JH-QC)
The paper is Edexcel 18th Jan 2007, Q3

It says:

The curve C has equation x=2siny
(a) show that the point P (?2,?/4) lies on C
(b) show that dy/dx=1/?2 at P

Edit: Symbols didn't work -- point P co-ordinates are Square Root of 2, Pi over 4; and dy/dx is 1/root 2
a) Show that 2sin(pi/4)=sqrt(2)

b) dy/dx = 1/(dx/dy)
Therefore you can differentiate 2siny with respect to y, divide 1 by the result and substitute in the value of y at P.

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