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# Official Edexcel C3 Discussion Thread watch

1. (Original post by Doughboy)
Yes, me too. But when I try substituting those answers back into the equations, I don't get the answer >_>

How do you prove the cos^x + sin^x = 1 though?

I didn't sub them back in! I'll try it again.

I think using the addition formulae. I've never come across it, but I did read somewhere that that's how you prove it (but I'm not sure). I'll try doing it, give me a few minutes.

Edit: I have it!

sin2x + cos2x=1

LHS:

sinxsinx+cosxcosx

which, if you think about it, is the same as: cos(x-x)

as x-x=0 therefore, it's cos0, which is 1.

or you could use Pythagoras and the unit circle, basically, where the hypotenuse is 1 etc.

if we ever have to prove it, i'm going to guess that the addition method would be preferred.
2. Good luck to everyone tomorrow

S2 was good today hope everyone did well
3. (Original post by ishta)

can some body help me out with parts B D and E
For B, you need to rearrange the derivative of y for x.

If you get stuck, the main trick is knowing that:

e^(1-4x) = 1/[8root(x)]

Is the same as saying

e^(4x-1) = [8root(x)]
4. (Original post by Doughboy)
Yes, me too. But when I try substituting those answers back into the equations, I don't get the answer >_>

How do you prove the cos^x + sin^x = 1 though?

Sin^x+cos^x=1?
Is that even possible? Never seen that in my life!
5. (Original post by Get Cape.Wear Cape.Fly.)
What paper is this from?

for b) find x?
Ok, for d) sub the upper and lower boundaries of your x4 value into the original equation.
for e) just find x1, x2, x3 etc and write down what happens. It will probably diverge(?) (not come to a constant number)

This is from Solomon paper C

Thanks for the reply
6. (Original post by ishta)
This is from Solomon paper C

Thanks for the reply
Oh thanks
btw I think my b) suggestion is wrong
7. the half-angle formulae, what do we need to be able to do with them. do we need to be able to prove them?
8. (Original post by Superman_Jr)
Sin^x+cos^x=1?
Is that even possible? Never seen that in my life!
That was a typo. I meant sin^2[x] + cos^2[x] = 1.
9. (Original post by unamed)
the half-angle formulae, what do we need to be able to do with them. do we need to be able to prove them?
I guess. The half angle formulae are just an extension of double angle. Nothing too difficult.
10. (Original post by Doughboy)
I guess. The half angle formulae are just an extension of double angle. Nothing too difficult.
Hopefully they won't come up, for some reason, I hate them.
11. (Original post by indie_couture)
Getting quite worried about this exam. Been revising for my resit for Biology last 2 days, done very little C3. As soon as I come home today from the exam I will be revising maths like all afternoon/evening and morning.

Here are some questions I got out of a P2 book. I am not sure what to do with them. Anyone fancy doing them?

1) find values for 0-360 for which:
7cosx+sinx=5
I though about using the RCosx, Rsinx but didnt get the right answer,

2) solve for 0-360
2cos(x+50)=sin(x+40)
Im thinking i should use addition formulaes but then didnt know what to do.

3) solve for 0-pi
3sinx+sinx=sin2x
do i used sin2x=2sinAcosB here? then how do i get just sin?

4) sinx=cos^2x for 0-360

i just dont seem to be able to do trig anymore!

I will probably be on here loads later with lots of questions! xxx
Why didn't you post the answers

I finally figured out where I went wrong in (1). Is x = 53.3, 323.3?

I'll go do 2, 3 and 4 now.
12. (Original post by Doughboy)
Why didn't you post the answers

I finally figured out where I went wrong in (1). Is x = 53.3, 323.3?

I'll go do 2, 3 and 4 now.
since I did the same as you, mind telling me where we went wrong? {I can't be bothered any more}
13. Can anyone help me quickly do question 1b of the June 2007 paper?

The markscheme's no help

EDIT: No worries, just being totally stupid
14. (Original post by unamed)
since I did the same as you, mind telling me where we went wrong? {I can't be bothered any more}
Well, I don't know about you, but:

I had tan(alpha) as 1/7. It was supposed to be 7/1. That's it o.o
15. (Original post by Doughboy)
Well, I don't know about you, but:

I had tan(alpha) as 1/7. It was supposed to be 7/1. That's it o.o
I put it as 1/7 too, why is it 7/1? isn't cos(alpha) 7 and sin(alpha) 1?
16. Why are the questions in the Heinemann Edexcel Textbook so hard compared to the real exam questions ?
17. Iv done 4 solomon papers only, since i started the course very late, but i would say compared to the other units (c1 c2 s1 s2) the solomon papers for c3 are not that hard. Plus, some of the questions in solomon are really weird (not difficult) and i doubt if Edexcel would use such questions...
18. (Original post by uer23)
Why are the questions in the Heinemann Edexcel Textbook so hard compared to the real exam questions ?
Good point. But I kind of like the fact that they are so hard.. when i finished the book and started practising the past edexcel papers i felt quite relaxed.
19. (Original post by ahnaf.c)
Good point. But I kind of like the fact that they are so hard.. when i finished the book and started practising the past edexcel papers i felt quite relaxed.
This really. They over prepare you on purpose so you find the exam easier, I think it's a good thing.
20. (Original post by ahnaf.c)
Good point. But I kind of like the fact that they are so hard.. when i finished the book and started practising the past edexcel papers i felt quite relaxed.
lol you have a point too about it making you confident and ready to face the exam questions. But I was just stressing about nothing when I was using the book, then coming to the exam questions they're piss easy. I couldve use that precious time doing something else/revising for another subject.

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