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Edexcel C3,C4 June 2013 Thread

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Reply 2800
Original post by Story
Hey guys I know im probably just missing something basic but...

If you you square 1/2sin theta cos theta, how do you get 4/4cos^2theta sin^2theta,

I get the bottom part but not how you get the 4 on top?


Anyone?
Original post by yaboy
I always simplify my direction vectors to the smallest whole numbers, because for one its make it easier to work with and 2 the markscheme usually right it with it there. As for your values for lambda it wont make a difference at all, when you need to find a certain point on the vector for example you will achieve a different lambda but it will be the right one when considering whether you simplified your direction vector or not. Basically it makes no difference.


thank you, guess I made a mistake then!
Original post by Story
Anyone?


Well its wrong.
Substituting any value for theta contradicts the 4/4.....expression. Its wrong. From where is this?

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Original post by Story
Anyone?

Where is this question from?
If we had sin(x+pi/3)=1 with the interval being 0<= x <=2pi,
how would the interval change?
Reply 2805
Original post by StUdEnTIGCSE
Well its wrong.
Substituting any value for theta contradicts the 4/4.....expression. Its wrong. From where is this?

Posted from TSR Mobile


Original post by Anonymous1717
Where is this question from?


If you Youtube Core 3 Edexcel June 2012 q)5)...its on Maths247's channel? As he is doing the working out, it may just be a mistake then?

If somebody could explain it to me I would appreciate it!
(edited 10 years ago)
Reply 2806
Original post by nm786
reciprocate the denominator and times it by the numerator. If the denominator's an integer (a) then multiply numerator by 1/a.

Sorry to be a pain but do you mind giving me an example just so I have it crystal clear?
Reply 2807
C3 is basically 3sf unless told otherwise right?
Reply 2808
Original post by alygirl
Sorry to be a pain but do you mind giving me an example just so I have it crystal clear?

sure, this is GCSE Maths tbh: 1/2 / 1/4 = 1/2 * 4/1 = 4/2 = 2, 1/2 / 4 = 1/2 * 1/4 = 1/8 (because reciprocal of 4 = 1/4)
(edited 10 years ago)
Reply 2810
Original post by Story
If you Youtube Core 3 Edexcel June 2012 q)5)...its on Maths247's channel? As he is doing the working out, it may just be a mistake then?

If somebody could explain it to me I would appreciate it!


There was a 4 in the numerator to begin with, he just multiplies by that 4
Reply 2811
Just say a questions give y=ln3t, how do you know if the (3t) is in brackets or just the 3 is in brackets as I remember one one question they did not give it brackets what do you assume then? As the answer was dy/dx = ln(3) but it did not give brackets to just the 3? I hope this made some sense.
Reply 2812
Original post by Mallika
If we had sin(x+pi/3)=1 with the interval being 0<= x <=2pi,
how would the interval change?


it wouldn't

some people choose to write the interval as pi/3<x<7pi/3 before they take away their pi/3 to the answers but i just think thats a hassle
Reply 2813
Original post by Max28
There was a 4 in the numerator to begin with, he just multiplies by that 4


I get it now. How did I miss it?

Just to be clear Its because cosec2theta=1/sin2theta
cosec2theta=1/2sintheta costheta, then you square this to get cosec^2 2theta = 1/4sin^2thetacos^2theta, etc?
Reply 2814
Original post by Story
I get it now. How did I miss it?

Just to be clear Its because cosec2theta=1/sin2theta
cosec2theta=1/2sintheta costheta, then you square this to get cosec^2 2theta = 1/4sin^2thetacos^2theta, etc?


That is correct :smile:
Original post by usycool1
Well, the graph is a translation of the graph for 10 t 60 (the graph is "shifted" to the right by 60). So, the the translated graph is f(t - 60).

So the equation is:

T = 5 + e0.0124(t60)e^{-0.0124(t-60)}

Then play around with it a bit using some rules you know for exponentials and you should get it. :smile:



They haven't really equated coefficients.

Thanks!
Reply 2816
Even though I know the exams tomorrow, I cant be bothered to revise.
How can completing the square lead to the range?
For example g(x)=x^2 +2ax+2, the range is g(x) is greater than or equal to 2-a^2. How did they get this from completing the square?

http://www.school-portal.co.uk/GroupDownloadFile.asp?GroupId=1152244&ResourceId=3992025
Reply 2818
Very best of luck with the C3 exam tomorrow everyone, dont forget it starts at 9.00, not 9.30, i made a mistake thinking my chemistry exam was at 9.30 last week and actually arrived late missed the start, like 10 mins of it. Anyway i was wondering if anyone had any good exam tips/strategy for this c3 exam. On a personal note and not wishing not be immodest at all i got 92 ums in jan c3, but thought i might as well resit it and try and get 100ums(since a* is average 90% ums in c3/c4), my revision strategy has been just doing solomon papers, infact the last edexcel paper i did was in january!, i have been getting around 90% on these solomon papers. i really would love to get an A* in maths, C4 is harder than C3 so anyone any tips.
Original post by Anonymous1717
How can completing the square lead to the range?
For example g(x)=x^2 +2ax+2, the range is g(x) is greater than or equal to 2-a^2. How did they get this from completing the square?

http://www.school-portal.co.uk/GroupDownloadFile.asp?GroupId=1152244&ResourceId=3992025


The range represents what the y-values go between. g(x) is a positive quadratic, so it has a minimum. By completing the square, you find the coordinates of that minimum, therefore telling you what g(x) has to be greater than or equal to :smile:

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