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AQA A2 Mathematics MPC4 Core 4 - 9th June 2015 [Discussion & unofficial markscheme] Watch

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    (Original post by mamacita)
    I squared both sides so I could try and rearrange so I only have cos
    Out of interest, which is signified as being correct?


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    (Original post by CD223)
    Out of interest, which is signified as being correct?


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    there is no mark scheme annoyingly! it's from a revision guide i'm using and it suggests doing the tan method, but I don't understand why squaring both sides and rearranging doesnt work too. It gives you the same values as the tan method, but also two more (for 0-360), and I don't know what would be accepted if it were to come up
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    (Original post by mamacita)
    there is no mark scheme annoyingly! it's from a revision guide i'm using and it suggests doing the tan method, but I don't understand why squaring both sides and rearranging doesnt work too. It gives you the same values as the tan method, but also two more (for 0-360), and I don't know what would be accepted if it were to come up
    Wouldn't squaring it produce additional solutions?


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    (Original post by mamacita)
    Attachment 414579
    Right, I don't know if I'm just being stupid here....
    But the two ways I do this question I get different solutions? Does anyone know what I'm doing wrong?
    You should do it via the tan method, the reason why you have got two more answers for the first method is if you strip it from all the complex maths you have basically done something like this:
    It is given that x=2
    Squaring both sides I can show that x^2 = 4
    Taking the square root x= -2, 2
    But this is not necessarily true, in this case x=2 and not -2

    Does this help to explain? You have ended up with two values as by squaring and taking the square root again, it has given you both positive and negative values, you could have continued your argument one to show this: Name:  ImageUploadedByStudent Room1433165187.816117.jpg
Views: 125
Size:  44.4 KB which would give you your two extra values, but these are not the correct answers, try plugging your two extra values into the equation and they will not work.


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    (Original post by mamacita)
    Attachment 414579
    Right, I don't know if I'm just being stupid here....
    But the two ways I do this question I get different solutions? Does anyone know what I'm doing wrong?
    Is that from a paper?



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    (Original post by mamacita)
    there is no mark scheme annoyingly! it's from a revision guide i'm using and it suggests doing the tan method, but I don't understand why squaring both sides and rearranging doesnt work too. It gives you the same values as the tan method, but also two more (for 0-360), and I don't know what would be accepted if it were to come up
    Squaring it will produce more solutions than are true for the original equation.
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    (Original post by jjsnyder)
    You should do it via the tan method, the reason why you have got two more answers for the first method is if you strip it from all the complex maths you have basically done something like this:
    It is given that x=2
    Squaring both sides I can show that x^2 = 4
    Taking the square root x= -2, 2
    But this is not necessarily true, in this case x=2 and not -2

    Does this help to explain? You have ended up with two values as by squaring and taking the square root again, it has given you both positive and negative values, you could have continued your argument one to show this: Name:  ImageUploadedByStudent Room1433165187.816117.jpg
Views: 125
Size:  44.4 KB which would give you your two extra values, but these are not the correct answers, try plugging your two extra values into the equation and they will not work.


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    That's great I understand now, thanks!
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    (Original post by CD223)
    Squaring it will produce more solutions than are true for the original equation.
    Thanks! I understand now
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    (Original post by JF2013)
    Is that from a paper?



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    No, from a booklet my school made for the topic, so the teachers came up with the questions I think
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    (Original post by mamacita)
    No, from a booklet my school made for the topic, so the teachers came up with the questions I think
    Do you have a digital version of the booklet?


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    (Original post by CD223)
    Do you have a digital version of the booklet?


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    no sorry
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    (Original post by mamacita)
    no sorry
    No worries! Hope revision is going well. Are you doing many C3 papers before Friday?


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    (Original post by CD223)
    No worries! Hope revision is going well. Are you doing many C3 papers before Friday?


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    I've only done a few, last week was the first time I had looked at C3 since november of last year and I forgot there were some tricky bits! I'm resitting FP1 on friday too so i'm trying to balance revising for that and C3 but I think they're both going well. How about you?
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    (Original post by mamacita)
    I've only done a few, last week was the first time I had looked at C3 since november of last year and I forgot there were some tricky bits! I'm resitting FP1 on friday too so i'm trying to balance revising for that and C3 but I think they're both going well. How about you?
    Woah that's a long time!! Well done for getting back into it.

    I'm gonna do the 2014 papers and the pilot papers as prep now


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    (Original post by CD223)
    Woah that's a long time!! Well done for getting back into it.

    I'm gonna do the 2014 papers and the pilot papers as prep now


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    I keep forgetting to do the pilots I hope I find time for them done an S2, M1, C3, C4 and physics paper today my head is all over the place hahah
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    (Original post by CD223)
    Woah that's a long time!! Well done for getting back into it.

    I'm gonna do the 2014 papers and the pilot papers as prep now


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    what are pilot papers?

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    (Original post by the_googly)
    what are pilot papers?

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    if you get full marks in them you are a fully qualified pilot ...
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    (Original post by TeeEm)
    if you get full marks in them you are a fully qualified pilot ...
    Yes, and you're off to a flying start for this year's exam... *Badum Tss*


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    (Original post by mamacita)
    I keep forgetting to do the pilots I hope I find time for them done an S2, M1, C3, C4 and physics paper today my head is all over the place hahah
    That's intense! What board are you on for physics!?


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    (Original post by the_googly)
    what are pilot papers?

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    They were posted on the C3 thread:

    http://www.thestudentroom.co.uk/show...7#post56451827
 
 
 
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