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

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Sorry for all this guys but I've gone wrong again 😑😑 ImageUploadedByStudent Room1432740492.313745.jpg

Sorry it's a bit messy :/
On the markscheme it said to split it into 1/15 and xroot(2x-1) but surely there's a way to do it if I didn't?
:/
It's from June 2012 q8b

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Reply 641

EmilyC96

ImageUploadedByStudent Room1432740781.496360.jpg

Can someone explain to me the method of getting the minimum/max values of x (2b) for everything as I don't know any of those bits as don't think my teacher explained it :/ just using question 2b from jan 09 to give you an idea of the questions I mean? Thanks for everyone's help today!

I've done 2a if that helps and got root10sin(x-1.25)

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(edited 8 years ago)

Reply 642

CD223

Original post by EmilyC96

Sorry for all this guys but I've gone wrong again 😑😑 ImageUploadedByStudent Room1432740492.313745.jpg

Sorry it's a bit messy :/
On the markscheme it said to split it into 1/15 and xroot(2x-1) but surely there's a way to do it if I didn't?
:/
It's from June 2012 q8b

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ImageUploadedByStudent Room1432741465.592335.jpg

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Reply 643

CD223

Original post by EmilyC96

ImageUploadedByStudent Room1432741654.032789.jpg

Just as cos theta alternates between -1 and 1, your expression will alternate between root 10 and negative root 10.

When looking for a minimum, set the expression you've just worked out to equal the negative value of R.

When looking for a maximum, set the expression you've just worked out to equal the positive value of R.

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Reply 644

Jimmy20002012

Original post by CD223

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How do you exactly know not to take the 15 up as well when separating variables?

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Reply 645

CD223

Original post by Jimmy20002012

How do you exactly know not to take the 15 up as well when separating variables?

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You can take the 15 up too. It will just be slightly harder. Keep it outside the integral for the remainder of calculations :smile:

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Reply 646

Tiwa

I somehow managed to get 2/4 mark on Q6 b ii of the June 2014 C4 paper by purely guessing. xD

Reply 647

CD223

Original post by Tiwa

I somehow managed to get 2/4 mark on Q6 b ii of the June 2014 C4 paper by purely guessing. xD

:L which question was that? Vectors?

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Reply 648

Tiwa

Original post by CD223

:L which question was that? Vectors?

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Yep! I took me a while to understand the question. even then, I made an educational guess.

Reply 649

CD223

Original post by Tiwa

Yep! I took me a while to understand the question. even then, I made an educational guess.

Oh right! Do you get it now?

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Reply 650

CD223

Where do they get a solution of 90 degrees from? I thought cotx couldn't equal zero?

I got the other solutions, just didn't know 90 degrees was one?

ImageUploadedByStudent Room1432818550.450692.jpg

ImageUploadedByStudent Room1432818550.450692.jpg

EDIT: Oops, got my x and y the wrong way around. Never mind :colondollar:

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(edited 8 years ago)

Reply 651

a123a

Original post by CD223

Where do they get a solution of 90 degrees from? I thought cotx couldn't equal zero?

I got the other solutions, just didn't know 90 degrees was one?

ImageUploadedByStudent Room1432818550.450692.jpg

EDIT: Oops, got my x and y the wrong way around. Never mind :colondollar:

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Write Cotx as cosx/sinx

Reply 652

CD223

Original post by a123a

Write Cotx as cosx/sinx

In which case

\cos x = 0

and

x = 90^{o}

?

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Reply 653

a123a

Original post by CD223

In which case

\cos x = 0

and

x = 90^{o}

?

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Yes.
I remember doing this question last year.
Edit: I could be wrong though.

Reply 654

CD223

Original post by a123a

Yes.
I remember doing this question last year.
Edit: I could be wrong though.

Oh right thanks!

Is this an acceptable way of showing the two tangents meet on the x axis?

(Jan 13 Q4 a ii)

ImageUploadedByStudent Room1432819401.624075.jpg

ImageUploadedByStudent Room1432819401.624075.jpg

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Reply 655

Stepidermis

Original post by a123a

Yes.
I remember doing this question last year.
Edit: I could be wrong though.

You're right :smile:

It's like how y=(x)/(2x-3) has an asymptote at y=0, but y can still =0 when the numerator is 0, if that makes sense... Sort of like a special case

Reply 656

Stepidermis

Original post by CD223

Oh right thanks!

Is this an acceptable way of showing the two tangents meet on the x axis?

(Jan 13 Q4 a ii)

ImageUploadedByStudent Room1432819401.624075.jpg

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If this is the question I'm thinking of, you need to show that y=0 rather than substituting y=0 into the equation.

i.e. you end up with two simultaneous equations where if you add them together you are given y=0.

Hope this helps :smile:

Reply 657

CD223

Original post by Stepidermis

You're right :smile:

It's like how y=(x)/(2x-3) has an asymptote at y=0, but y can still =0 when the numerator is 0, if that makes sense... Sort of like a special case

How is that even possible 😁

Surely the equation breaks down?

Maths blows my mind.

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Reply 658

CD223

Original post by Stepidermis

Thanks! Are there no alternative methods? My thinking was, if I set y=0 in both equations and that gives the same x co ordinate for both, surely that means they both intersect at the x axis?

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Reply 659

Stepidermis

Original post by CD223

There must be other ways of showing that y=0, however in this instance I don't think your way works because in the question they have told you that q cannot equal 0 but they haven't given you a restriction for p (correct me if I'm wrong).

So the fact that you've found two equivalent expressions for x in this case is nullified by the fact that they both contain (q/p), as if p=0 then they don't intersect as this would instead be an asymptote, does that make sense?