This discussion is now closed.

Check out other Related discussions

Edexcel A2 C3 Mathematics 12th June 2015

Reply 2080

JizzaStanger

4

Original post by imedico10

Can someone explain 7b please

This is how I explained it to the last guy. But seriously... go to bed.

Original post by JizzaStanger

First do a sketch to determine roughly where the graphs touch. Because the one of the functions is |f(x)|, you use the sketch to determine whether you're in the section where |f(x)| = -f(x) or the section where |f(x)| = f(x).

Now you've determined that with a sketch (from the fact that you would otherwise have to take the square root of a negative number, it's in the region where |f(x)| = -f(x) ). You should now set -f(x)=g(x), and follow the method again. It will get you k = +/- 2a.

You can determine whether k = 2a or -2a by using your sketch again. The question tells you that g(x) cuts |f(x)| at another point, Q. You'll find that one value of k makes it impossible for the curves to cross at Q and that one makes it possible. The one that makes it possible is, of course, 2a.

I hope this clears it up!

(edited 8 years ago)

Reply 2081

Hudl

16

c3 june 13 was anal without lube, I feel unprepared now after doing that paper having done all the solomon papers and all the edexcel papers pre-june 13

Reply 2082

JizzaStanger

4

Original post by imedico10

Can someone explain 7b please

Sorry... I need to elaborate on 'the method.'

Original post by JizzaStanger

First do a sketch to determine roughly where the graphs touch. Because the one of the functions is |f(x)|, you use the sketch to determine whether you're in the section where |f(x)| = -f(x) or the section where |f(x)| = f(x).

Now you've determined that with a sketch (from the fact that you would otherwise have to take the square root of a negative number, it's in the region where |f(x)| = -f(x) ). You should now set -f(x)=g(x), and follow the method again. It will get you k = +/- 2a.

The method is as follows: Set -f(x)=g(x). Because g(x) is a tangent to |f(x)| in the region where |f(x)|=-f(x), g(x) will only touch |f(x)| and not cross it at P. This means the equation -f(x)=g(x) (it will be a quadratic) will have one repeated solution. This means the discriminant of the equation = 0. Solve the equation: discriminant = 0 to find k.

You can determine whether k = 2a or -2a by using your sketch again. The question tells you that g(x) cuts |f(x)| at another point, Q. You'll find that one value of k makes it impossible for the curves to cross at Q and that one makes it possible. The one the makes it possible is, of course, 2a.

I hope this clears it up!

(edited 8 years ago)

Reply 2083

marco cb

2

Original post by veniceswan

Hi does anyone know when the graph is shifting to the right and left or up and down? For example, for normal equations like 3x, does it means stretch up and down by a factor of 3?
Also can somebody help me with this 6c on 2014(r). I don't understand why 2x doesnt get why isnt 2x squared?
Thanks

f(x+a) is shift to the left by a
f(x-a) is shift to the right by a
f(x)+a is shift upwards by a
f(x)-a is shift downwards by a

-f(x) is reflection in x axis
f(-x) is reflection in y axis

af(x) is a vertical stretch by a
1/a f(x) is a vertical compression by a

f(ax) is a horizontal compression by a
f(1/a x) is a horizontal stretch by a

and for 6c in 2014
its because g(x)+g(x^2)+g(x^3)
not g(2x)+g(2x^2)+g(2x^3)

only the x is getting squared, not the number in front of it.

Reply 2084

jmuz

2

Original post by Hudl

c3 june 13 was anal without lube, I feel unprepared now after doing that paper having done all the solomon papers and all the edexcel papers pre-june 13

take a deep breathe…
i nearly cried when i done it……….

then i check boundaries

50 for an A
57 for an A*
with a special notice on the mark scheme basically saying 'sorry we f*ked everyone over

Reply 2085

A1d9a9m7

1

can't sleep so thought I may as well browse this for inspiration haha

Posted from TSR Mobile

Reply 2086

marco cb

2

Original post by Hudl

c3 june 13 was anal without lube, I feel unprepared now after doing that paper having done all the solomon papers and all the edexcel papers pre-june 13

Yep, currently on q6 on that paper... damn, it has demotivated me quite a bit. Even the low grade boundaries wouldn't have saved me so lemme pray that edexcel is nice this year.

(edited 8 years ago)

Reply 2087

TeeEm

19

Original post by Hudl

c3 june 13 was anal without lube, I feel unprepared now after doing that paper having done all the solomon papers and all the edexcel papers pre-june 13

..

https://docs.google.com/file/d/0B1ZiqBksUHNYNjhuUFdKRnpnQVd4Yzk4a2czR055Q2F2TlBJ/edit?pli=1
can somone explain 8a?
please
i dont get it

(edited 8 years ago)

Reply 2089

marco cb

2

So people who are still here, what time are y'all planning to catch some sleep?

Reply 2090

suyoof123

2

Original post by marco cb

So people who are still here, what time are y'all planning to catch some sleep?

This is the first exam im considering staying up..got 7 more PP to skim through...

Reply 2091

TeeEm

19

Original post by marco cb

So people who are still here, what time are y'all planning to catch some sleep?

they are not!!!
it is not a good idea to catch some sleep before an exam ...

Reply 2092

TeeEm

19

Original post by suyoof123

This is the first exam im considering staying up..got 7 more PP to skim through...

hopefully you catch some sleep during the exam ...

Reply 2093

Tplox

2

https://docs.google.com/file/d/0B1Zi...lBJ/edit?pli=1
its the jan 15 c34 ial paper
can somone explain 8a?
please
i dont get it

Reply 2094

suyoof123

2

Original post by TeeEm

hopefully you catch some sleep during the exam ...

Yeah , my random head movements sleeping with the pen in my hand will draw the correct solutions

Ok ok mr grumpy cat I'll sleep in 5 mins

:biggrin:

Reply 2095

Hudl

16

Got a question from that june 13 paper, not gone to bed yet as trying to understand where I flawed. There are a few algebraic errors due to silly mistakes. Sill managed an A* but only got 58.

I'm confused as to why you found the maximum value for the denominator, if we want the minimum value for V shouldnt the value on the denominator be as small as possible so -25 in other words, that way you get 21/-25 which is smaller than 21/25?

for the velocity question part b q8 June 2013

EDIT

Also within the range we're given 0 < X < 150 we cant have cosX as 1

(edited 8 years ago)

Reply 2096

Boop.

12

Original post by Tplox

https://docs.google.com/file/d/0B1Zi...lBJ/edit?pli=1
its the jan 15 c34 ial paper
can somone explain 8a?
please
i dont get it

Put t=0 into the function to get the maximum value of V (=23000) we know that as t goes to infinity, e^-0.1t and e^-0.2t go to zero, hence the graph's asymptote is at V=0+0+1000, V=1000 is the minimum value of V, but V only reaches 1000 at infinity so you must put V>1000 not V>=1000, so final answer is 1000<V=<23000