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

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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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

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?

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?

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

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: 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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Squaring it will produce more solutions than are true for the original equation.

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

Do you have a digital version of the booklet?


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no sorry

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?

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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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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if you get full marks in them you are a fully qualified pilot ...

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

what are pilot papers?

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