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# Edexcel A2 C3 Mathematics 12th June 2015 watch

1. (Original post by SeanFM)
Addition formulae, P124 of the textbook.
I've used the addition formulae. I get 2sinxcosx + 2sinycosy. How do they get from this to:
2sin(x+y)cos(x-y)
2. (Original post by Oxyfrost)
Hello, can anyone help me? I'm stuck on C3 Solomon paper C Question four. Attached is the question and mark scheme. It's a trig proof question. What I can't figure out, is for example, the numerator is sin2x + sin2y. The first step of the mark scheme sets the numerator as
2sin(x + y)cos(x-y)
How did they get to this? It's driving me insane! Really thrown my confidence, day before exam :/

use these
3. (Original post by Raj_B961)
quick question, how do we find the maximum or minimum value in trig questions??????????????????????? ???????????????????????????????? ???????????????????????????????? ??????????????????
The maximum of sinx or cosx is 1. So if you've got a harmonic form question, the maximum is R*1.
4. Need help on part b.
Thanks

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5. (Original post by JizzaStanger)
set the two functions equal to each other to get an equation for their points of intersection. It should be a quadratic in x. Since they curves are tangential, you know this equation only has one solution. This means the discriminant of the equation is zero. You'll then get an equation you can solve for k.
Fantastic!! Thank you good luck tomorrow

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6. (Original post by Oxyfrost)
I've used the addition formulae. I get 2sinxcosx + 2sinycosy. How do they get from this to:
2sin(x+y)cos(x-y)
I've used the wrong name, I'm terribly sorry.

It's the factor formulae. SinP + SinQ = 2sin((P+Q/2)cos((P-Q)/2), so putting in P=2x and Q=2y gives the result.

It *is* in the formula booklet, so don't worry.
(Original post by frozo123)
It's really nice of you spending your evenings during exam week to help people out
You're too kind Good luck with your exam, you and everyone else
7. (Original post by TeddyKC)
Fantastic!! Thank you good luck tomorrow

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8. (Original post by JayGreen)
I have done most of the c3 papers and to my knowledge factor formulae has never come up (I might be wrong though so dont hold me to that)
Only ones I havent done are June 12 and Jan 13 & ive never seen it so I think were good
9. (Original post by AbubakarB)

use these
thanks. We've never used these ones in class examples. Foolish me didn't even consider them.
10. (Original post by Oxyfrost)
The maximum of sinx or cosx is 1. So if you've got a harmonic form question, the maximum is R*1.
11. When was the last time they asked for factor formula proof?
I have an inkling

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12. how would you do 6aii)

https://07a69ccf283966549a9350d1a669...%20Edexcel.pdf
13. (Original post by JizzaStanger)
My apologies, I was trying to tell you how to do it without having done it myself! If you do it as I suggest you will indeed have to take the square root of a negative number!

First do a sketch to determine roughly where the graphs touch. Because the one of the functions is |f(x)|, you use the sketch to determine whether you're in the section where |f(x)| = -f(x) or the section where |f(x)| = f(x).

Now you've determined that with a sketch (from the fact that you would otherwise have to take the square root of a negative number, it's in the region where |f(x)| = -f(x) ). You should now set -f(x)=g(x), and follow the method again. It will get you k = +/- 2a.

You can determine whether k = 2a or -2a by using your sketch again. The question tells you that g(x) cuts |f(x)| at another point, Q. You'll find that one value of k makes it impossible for the curves to cross at Q and that one makes it possible. The one the makes it possible is, of course, 2a.

I hope this clears it up!
14. (Original post by TeddyKC)
Fantastic!! Thank you good luck tomorrow

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I actually sat it last year; I'm doing a bit of good will, but thanks anyway
15. (Original post by Bustamove)
wait whaaa?
what formula is that? When is it used?
thanks
I think I learnt it in FP1 or FP2, can't remember
16. If you're doing a transformation of a function with several parts, when do you apply the modulus ? At the end or at the start?

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17. so proof by contradiction is in the specification but theres never been any questions on it? what could they ask us to prove?
18. (Original post by frozo123)
how did you find the chem yesterday?
it was kind of hard , how did you find it ?
19. (Original post by Maham88)
it was kind of hard , how did you find it ?
I liked A and C, made loads of mistakes on B hopefully 78/80though
cba for Unit 5gonna get like a C on it lol
20. (Original post by JizzaStanger)
I actually sat it last year; I'm doing a bit of good will, but thanks anyway
Hey can you explain the last part I'm really really confused

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