Edexcel C3 (20/06) Revision Thread Watch

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violet
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#141
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#141
(Original post by Widowmaker)
yep, or in the range x = a and x = b
I'll pretend you didn't say that or I'll die of confusion..

Thank you and thanks Sam
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samd
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#142
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#142
He is just saying that some fuctions go up and down. (like y = x2)

and a function can be defined as increasing within an certain interval like y = x2 in the interval between x = 1 and x = 6 is increasing, but between x = -5 and x = -1 it is decreasing.

(numbers just chosen at random to show the point, you could have had 65 and 108, and -47 and -32)
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Goody1
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#143
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#143
(Original post by Widowmaker)
sin5x + sinx
= sin(3x + 2x) + sin(3x-2x)
= sin3xcos2x + sin2xcos3x + sin3xcos2x - sin2xcos3x
= 2sin3xcos2x = 0

2sin3x = 0 OR cos2x = 0
sin3x = 0
3x = arcsin0, 180°+arcsin0, 360° + arcsin0
3x = 0°, 180°, 360°
x = 0°, 60°, 120°

cos2x = 0
2x = arccos0, 360° - arccos0,
2x = 90°, 270°
x = 45°, 135°

x = 45°, 60°, 120°, 135°

Ignore the values 0° and 180° since they aren't in range.
Unless the range is 0</=x</=pi
Thanks Very Much!!!
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samd
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#144
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#144
(Original post by Widowmaker)
2sin3x = 0 OR cos2x = 0
sin3x = 0
3x = arcsin0, 180°+arcsin0, 360° + arcsin0
3x = 0°, 180°, 360°
x = 0°, 60°, 120°
I know it makes no difference here, but shouldn't it be: 180 - arcsin0 not + ?
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nas7232
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#145
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#145
yep
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Christophicus
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#146
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#146
(Original post by samdavyson)
I know it makes no difference here, but shouldn't it be: 180 - arcsin0 not + ?
hmm, yes it makes no difference.
but when θ is acute it lies in quadrant 1. tan θ is positive in quadrant 1 and quadrant 3, so tanθ = tan(180+θ)
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samd
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#147
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#147
(Original post by Widowmaker)
hmm, yes it makes no difference.
but when θ is acute it lies in quadrant 1. tan θ is positive in quadrant 1 and quadrant 3, so tanθ = tan(180+θ)
I think you mean sinθ = sin(180 - θ).
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Christophicus
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#148
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#148
(Original post by samdavyson)
I think you mean sinθ = sin(180 - θ).
nope I mean tan.
e.g. tan 20 = tan 200
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samd
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#149
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#149
(Original post by Widowmaker)
nope I mean tan.
e.g. tan 20 = tan 200
Yes but in the question it is arcsin!
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Christophicus
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#150
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#150
(Original post by samdavyson)
Yes but in the question it is arcsin!
:banghead: :banghead: :banghead:
yes, then you are correct. lol
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samd
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#151
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#151
(Original post by Widowmaker)
:banghead: :banghead: :banghead:
yes, then you are correct. lol
lol.

But you are correct with tanθ = tan(180 + θ).

Do you prefer C3 or C2?
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Christophicus
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#152
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#152
(Original post by samdavyson)
lol.

But you are correct with tanθ = tan(180 + θ).

Do you prefer C3 or C2?
i like them both equally.
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ntrik
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#153
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#153
Hey heres a quick question:

xln3x - x - 1 = 0
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samd
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#154
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#154
(Original post by ntrik)
Hey heres a quick question:

xln3x - x - 1 = 0
How the hell do you do that? :eek:
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mackin boi
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#155
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#155
how do u do that????
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samd
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#156
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#156
(Original post by mackin boi)
how do u do that????
I just go round and round in circles.

It looks like sometime you might use iteration for.
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mackin boi
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#157
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#157
i think theres more 2 this Q
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samd
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#158
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#158
(Original post by mackin boi)
i think theres more 2 this Q
You get to: =>3xx = ex+1

And you find isolating the x impossible.
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ntrik
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#159
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#159
(Original post by samdavyson)
How the hell do you do that? :eek:
Damn I must be using the wrong approach then.

I have to prove that x = 1.66 to 3sf.

I've also got an interation formula which is xn+1 = (1/3)e^(1+(1/x)) where x0 = 2 but I dunno if that helps or anything.

Edit - Oh wait, does that mean I need to subsitute 1.66 into the equation to get a value that is close to 0?
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Christophicus
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#160
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#160
I did a similar question yesterday. I'll just post the link.

http://www.thestudentroom.co.uk/t123238.html

You have to use iteration at c3 level. There's not another way that i'm aware of.
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