OCR C4 (not mei) 18th June 2013 revision

Original post by adam17

you know cos4x = 2cos^2(2x) -1 from C3
rearrange to cos4x + 1 = 2cos^2(2x)
then 0.5cos4x + 0.5 = cos^2(2x)
:smile:

Thank you

c4 june 2009 q9.JPG90.3KB

Reply 141

bbm100

i think someone else has asked for this question already but i don't understand why the answer to part 1 is 20/k1

i've attached the question

june 2009

(edited 10 years ago)

c4 june 2009 q9 answer.JPG58.5KB

Reply 142

jassi1

2

Original post by Hello_ImJess

Help with question 4 please

ImageUploadedByStudent Room1371465715.798886.jpg

The reason why using

x= \frac{1}{3} sin \theta

is useful is because this helps us utilise the Pythagorean identity

sin^2x +cos^2x =1

to simplify the denominator. This makes it easier to integrate because the denominator becomes much more simple.

Reply 143

Original post by Hello_ImJess

Help with question 4 please

ImageUploadedByStudent Room1371465715.798886.jpg

there you go, hope that's the right answer :redface:

(edited 10 years ago)

Reply 144

eggfriedrice

16

Is it me or does C4 just loves putting little things to trip you up? Like the principle integration /differentiation etc isn't too bad but when you're setting up all the equations and you don't notice something cancels then you're screwed.
That's what I've been finding with the papers anyways.

Reply 145

Original post by bbm100

i think someone else has asked for this question already but i don't understand why the answer to part 1 is 20/k1

i've attached the question

june 2009

because its rising at K₁^oC/s..

As its rising 20^oC, it'll take 20/K₁ seconds.

I don't really know how to explain it.. imagine K = 3.
To rise 20 degrees, it'll take 20/3 seconds.

Reply 146

Original post by eggfriedrice

Is it me or does C4 just loves putting little things to trip you up? Like the principle integration /differentiation etc isn't too bad but when you're setting up all the equations and you don't notice something cancels then you're screwed.
That's what I've been finding with the papers anyways.

after doing so many papers (which are all pretty similar) you sorta just learn the little tricks etc. That's what I've found anyway!

Reply 147

JimmyA*

5

Original post by bbm100

i think someone else has asked for this question already but i don't understand why the answer to part 1 is 20/k1

i've attached the question

june 2009

Search it in youtube or search hegartydave and you should find a video on it :smile:

Reply 148

jassi1

2

Original post by bbm100

i think someone else has asked for this question already but i don't understand why the answer to part 1 is 20/k1

i've attached the question

june 2009

The heater causes the temperature to increase at k degrees per second:

therefore

\frac{d \theta}{d t} = k

You can solve this differential equation with the information given and hense answer the question.

OR

Because temperature increases at a constant rate the rate of change of temperature is given by

\frac{60-40}{t} = k

where t is the time taken for the increase. You may wish to think about this geometrically as a gradient of a straight line.

Reply 149

eggfriedrice

16

Original post by stirkee

after doing so many papers (which are all pretty similar) you sorta just learn the little tricks etc. That's what I've found anyway!

Haha yeah! I'm planning to do as many past papers today as I can and jot down all their little tricks. Sneaky C4.

Reply 150

Original post by eggfriedrice

Haha yeah! I'm planning to do as many past papers today as I can and jot down all their little tricks. Sneaky C4.

I'm pretty sure I know everything inside out.. my only downfall will be rushing and/or making stupid mistakes..

I find C4 easier than C3... I'm pretty sure I got over 90UMS in C3 so I'd hate myself if I screwed up my A* by mucking up C4.. lol.

but yeah I think (hope) i've seen all of the little tricks before!

Reply 151

eggfriedrice

16

Original post by stirkee

I'm pretty sure I know everything inside out.. my only downfall will be rushing and/or making stupid mistakes..

I find C4 easier than C3... I'm pretty sure I got over 90UMS in C3 so I'd hate myself if I screwed up my A* by mucking up C4.. lol.

but yeah I think (hope) i've seen all of the little tricks before!

Same actually, it took me a lot longer to understand C3 than C4. I got a B overall last year in Maths so I retook C1, C2, and C3 this exam season xD I'm predicted an A but now I'm greedy and want the A* >:
I love how M1/2 doesn't affect the A* though xD

Reply 152

Original post by stirkee

there you go, hope that's the right answer :redface:

I'm still a little confused. When you sub 1/3sin theta into 1 - 9x^2 you get 1-3sin^2theta. How did you get to the next line of working from there?

Posted from TSR Mobile

Reply 153

Original post by Hello_ImJess

I'm still a little confused. When you sub 1/3sin theta into 1 - 9x^2 you get 1-3sin^2theta. How did you get to the next line of working from there?

Posted from TSR Mobile

when you square 1/3sin theta you get 1/9sin^2theta.

multiply that by 9 to get sin^2theta.

1-sin^2theta = cos^2theta

get it? :smile:

Reply 154

Original post by eggfriedrice

Same actually, it took me a lot longer to understand C3 than C4. I got a B overall last year in Maths so I retook C1, C2, and C3 this exam season xD I'm predicted an A but now I'm greedy and want the A* >:
I love how M1/2 doesn't affect the A* though xD

I've found C3 much easier than C4 when learning it; its just since starting the past papers I've found C4 easier as the papers are all the same. I found that in C3 there's more random/hard stuff that they can throw at you but In C4 you know what is gonna come up every time.

Reply 155

jassi1

2

Original post by Hello_ImJess

I'm still a little confused. When you sub 1/3sin theta into 1 - 9x^2 you get 1-3sin^2theta. How did you get to the next line of working from there?

Posted from TSR Mobile

you get

1-sin^2\theta

Reply 156

Original post by stirkee

when you square 1/3sin theta you get 1/9sin^2theta.

multiply that by 9 to get sin^2theta.

1-sin^2theta = cos^2theta

get it? :smile:

Ahhhh got it, thank you

Posted from TSR Mobile

Reply 157

How would you integrate this?

ImageUploadedByStudent Room1371470840.451832.jpg

Reply 158

Original post by Hello_ImJess

How would you integrate this?

ImageUploadedByStudent Room1371470840.451832.jpg

(integral of) x+2-2/x+2

= (integral of) 1 - 2/x+2

= x - 2ln(x+2)

Reply 159

ninuzu

17

Original post by Hello_ImJess

How would you integrate this?

ImageUploadedByStudent Room1371470840.451832.jpg