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# Official Edexcel C3 Discussion Thread watch

1. How's everyone coming with practice?
2. good good....the only unit i am confident about really
3. better, i couldn't do differentiation the other day, couldnt see how they got the answer in the book but I am beginning to get it!!
Now to start trig. xxx
4. (Original post by Doughboy)
How's everyone coming with practice?
I haven't done any C3 this holiday but I'm very confident indeed
5. Ok, just done a Solomon paper, and the only thing that baffled me completely was an iterative formula question.

This is a stupid question, but just to double check. The question gave an iterative formula then said "Use the iterative formula with a suitable starting value to find the root of the equation f(x)=0 correct to 3sf." Do you just pick a number that looks to be vaguely close to the root for your value of x0 (sorry, the zero is supposed to be subscript but not sure how to do it) and go from there or is there some way to work out what x0 is? I've never done a question before that doesn't give you a value of x0 to start with so it just confused me a little.

Thank you
xxx
6. you choose a number that is within the interval if where the root lies in, eg if the root is in the interval 1 < x < 2, you choose a number between 1 and 2
7. (Original post by samir12)
you choose a number that is within the interval if where the root lies in, eg if the root is in the interval 1 < x < 2, you choose a number between 1 and 2
Ok thank you
8. Can someone help me with questions such as:

find the range of f-1

find the domain of f-1

I know its asking for the range/domain of the inverse but how do you work out the range/domain. What do they mean? xxx
9. (Original post by indie_couture)
Can someone help me with questions such as:

find the range of f-1

find the domain of f-1

I know its asking for the range/domain of the inverse but how do you work out the range/domain. What do they mean? xxx
A lot of the time when it asks for the range and domain of the inverse, they'll have already given you the range/domain of the original function in the question, and the range of the function is the domain of the inverse, and vice versa.

If not though, it might help to draw a graph and look at what what values are possible/impossible in the x direction to help you find the domain, and in the y direction to help you find the range

xxx
10. Thanks.

I was doing some trig this morning and had this random worksheet thing. A few of them I have no idea what to use e.g. double angle/addition formula etcc..

1. Solve Sin3θ - Sin θ = 0, for 0 ≤ θ ≤ 2π

2. Solve 2Sinθ = 1 + 3Cosθ, for 0 ≤ θ ≤ 2π

3. Solve Sin(θ+45◦) + Sin(θ+60◦) = 0, for 0-360 for this I know you use the addition formulae but what do you do when you have expanded it out and get like 1/2 x Cos to solve it? etc.

I have probably done them before but I seem to have not done as much maths revision as everything else and now am looking at questions and panicking!! xxx
11. for 1) you can do sin( 2θ + θ ) and expand it,

for 2) I'm not entirely sure, but what I did is divide both sides by cosθ, and then you have 2tanθ = secθ + 3 on the other, and recall tan^2θ + 1 = sec^2θ, so you can square 2tanθ = secθ + 3, (this is the bit I'm not sure about) and turn either tan^2θ into sec^2θ or vice versa.

for 3) sorry I cannot read the question properly
12. (Original post by samir12)
for 1) you can do sin( 2θ + θ ) and expand it,

for 2) I'm not entirely sure, but what I did is divide both sides by cosθ, and then you have 2tanθ = secθ + 3 on the other, and recall tan^2θ + 1 = sec^2θ, so you can square 2tanθ = secθ + 3, (this is the bit I'm not sure about) and turn either tan^2θ into sec^2θ or vice versa.

for 3) sorry I cannot read the question properly
This may sound stupid is the expansion of sin(2θ+ θ):
Sin2θCosθ+Cos2θSinθ
xxx
13. (Original post by indie_couture)
Sin3θ - Sin θ = 0
sin(x + 2x) - sinx = 0
sinxcos2x + sin2xcosx - sinx = 0
sinx(1 - 2sin^2(x)) + 2sinxcos^2(x) - sinx = 0
sinx - 2sin^3(x) + 2sinxcos^2(x) - sinx = 0
sinx - 2sin^3(x) + 2sinx(1 - sin^2(x)) - sinx = 0
sinx - 2sin^3(x) + 2sinx - 2sin^3(x) - sinx = 0
2sinx - 4sin^3(x) = 0
sinx - 2sin^3(x) = 0
sinx(1 - 2sin^2(x)) = 0
14. (Original post by Pheylan)
sin(x + 2x) - sinx = 0
sinxcos2x + sin2xcosx - sinx = 0
sinx(1 - 2sin^2(x)) + 2sinxcos^2(x) - sinx = 0
sinx - 2sin^3(x) + 2sinxcos^2(x) - sinx = 0
sinx - 2sin^3(x) + 2sinx(1 - sin^2(x)) - sinx = 0
sinx - 2sin^3(x) + 2sinx - 2sin^3(x) - sinx = 0
2sinx - 4sin^3(x) = 0
sinx - 2sin^3(x) = 0
sinx(1 - 2sin^2(x)) = 0
okay, thankyou xx
15. I have a request.

Sky sports used to use an opera tune all the time, especially during when they rounded up the champion's league at the end of the night.

It goes.

E D C# B B F# E F#
E D B A C# E D C# B
16. dw found it. "we took pelham" by deadly avenger.
17. Music video i saw a few days ago, could have sworn it was called reaction but searching for it I get nothing back. Kinda indy-ish singers a blonde with a black leotard on, got scientists in the music video. I cant really rememberm uch else...
18. Theres a song which sometimes plays on the Virgin Media On Demand thing, all i know is that its a man with an (I think) acoustic guitar, and for at least a part of the song, he sings "its alright its alright its alright" over a few times.

Anyone help me out?
19. Is there a specimen paper for this exam? If so, can someone give me the link to it please.
20. (Original post by Orwell)
Theres a song which sometimes plays on the Virgin Media On Demand thing, all i know is that its a man with an (I think) acoustic guitar, and for at least a part of the song, he sings "its alright its alright its alright" over a few times.

Anyone help me out?
Nine Crimes by Damien Rice?

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