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Edexcel A2 C3 Mathematics 12th June 2015

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Original post by Ripper Phoenix
square both sides and solve for x its easy :smile:


For mod equations, when can you NOT square both sides and what do you do then.
Original post by suyoof123
For mod equations, when can you NOT square both sides and what do you do then.


let me show you give me a minute :smile:
When you have to find out a in Rsin(x-a), do you use Sinx/Cosx or Cosx/Sinx ?
Cause most of the time I've needed to use Cosx/Sinx but it makes no sense to use it
Original post by Ripper Phoenix
no its c3

also i have a strong feelin that we may be asked to draw modulus graphs like

y=IX+2I +2 or something like that lol

i'm paranoid


And how exactly would you draw y=|x+2| +2 :hmmm:

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Original post by suyoof123
For mod equations, when can you NOT square both sides and what do you do then.


ImageUploadedByStudent Room1434013407.451249.jpg

See this 😋


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Original post by TheRaspberry
I am really confused when solving these mod equations; for the 2nd solution, how do you know which side to put the minus on, because I am pretty sure there have been questions where it has been required for it to be put on alternate sides (e.g the minus on the mod equation side, and then on the non-mod side (not on the same question!!))

Sorry if this is confusing, but any help would be really appreciated. If anyone could just talk me through part b, to determine on which side you would put the minus, the question being from the June 2014 (R) paper that would also be much appreciated. :smile:



see the post above i posted the solution. Hope you understand :smile:
Original post by it's a me, mario
And how exactly would you draw y=|x+2| +2 :hmmm:

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that is exactly why i asked because i dont know.. edexcel forces my brain to think in weird ways
Original post by Ripper Phoenix
that is exactly why i asked because i dont know.. edexcel forces my brain to think in weird ways


Draw graph of y = x, shift 2 units left, reflect negative values and shift 2 units up

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Original post by Ripper Phoenix
that is exactly why i asked because i dont know.. edexcel forces my brain to think in weird ways


I think i know actually

That graph is just built from the graph y=|x|

|x+2| would shift it left 2 units
+2 would shift it up two units

I think thats how you do it fam

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Original post by aersh8
Draw graph of y = x, shift 2 units left, reflect negative values and shift 2 units up

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Original post by it's a me, mario
I think i know actually

That graph is just built from the graph y=|x|

|x+2| would shift it left 2 units
+2 would shift it up two units

I think thats how you do it fam

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thought of it like that too thank you both :smile:
Original post by Ripper Phoenix


Thanks and you wouldnt put >/ (equals to ) or /< (equals to ) on this because if it were when equals or bigger/smaller than 0, then you would do that?.

Also originally I meant what happens if you have two mods on either side of the equation, would the squaring method still be viable.
Original post by it's a me, mario
I think i know actually

That graph is just built from the graph y=|x|

|x+2| would shift it left 2 units
+2 would shift it up two units

I think thats how you do it fam

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Pretty sure you need to shift it left before you do the modulus of it

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Original post by SeanFM
Ah, so you've got values like 10, 12 in the second quadrant?

If so, it's possible that they specified a domain, or that they're not interested in the bits to the left of the y axis but you probably wouldn't lose marks unless they specified the domain.



I think it is possible, if it was +alpha and you had it in the form -alpha then alpha would be a negative value.

Ah ok thanks! do you mind helping me with https://07a69ccf283966549a9350d1a66951a7bc96e2dc.googledrive.com/host/0B1ZiqBksUHNYZ0JQM1NRcmdHdXM/June%202013%20(R)%20QP%20-%20C3%20Edexcel.pdf 3c?
https://07a69ccf283966549a9350d1a66951a7bc96e2dc.googledrive.com/host/0B1ZiqBksUHNYZ0JQM1NRcmdHdXM/June%202013%20(R)%20QP%20-%20C3%20Edexcel.pdf

For 4b how do we know which value to use once we have done it with both a positive mod and negative mod?
Does anyone have a list of formulas we need to know off the top of our head?

especially the trig functions
Original post by mat1996
OMG, I can't believe i didn't see that. Thank you so much for your help :smile: but you know when I do it on the calculator it gives me -root3/9. Would examiners know this is equivalent or should i change it to the other answer (and how would I know this in the exam)


it is the same so no need to worry
Whoops sorry everyone, think I scared everyone with that question on mod inequalities!
Original post by adorablegirl1202


Think about cos and the values it takes between 0 and 2pi, and try to spot the values that only come up once, and then see how you can apply that to find the correct answer.

Original post by adorablegirl1202
https://07a69ccf283966549a9350d1a66951a7bc96e2dc.googledrive.com/host/0B1ZiqBksUHNYZ0JQM1NRcmdHdXM/June%202013%20(R)%20QP%20-%20C3%20Edexcel.pdf

For 4b how do we know which value to use once we have done it with both a positive mod and negative mod?


If you're asking about fg(1), then mod(-1) = 1.
Original post by bbadonde2
Just do the exam really slowly and check your answer after very question and then check everything again at the end. Just do that in a few past papers today and see if you come out any better?


Thanks for the advice I will make sure to do this
Original post by TheRaspberry
Whoops sorry everyone, think I scared everyone with that question on mod inequalities!


not really :wink:

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