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# Edexcel C2 20th May 2015 *Official Thread* watch

1. (Original post by yasmin#2)
am i the only one that doesnt feel prepared for this at all?
I swear you were the one who memorised all the proofs the other day haha
you'll do well chill
2. (Original post by IIEquinoxII)
i think you do R x 64 x 2
That's right, can you please explain how you did it?

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3. (Original post by Skygon)
Hey there, I would recommend learning the trignometric ratios for triangles with the angles ( 30, 60 and 90 ) as well ( 45, 45 and 90 ). They come in handy when tackling such questions..

Alright so, assuming you've already found y, which is 100 / x^2. To find the area of metal used, you're basically finding the area of all faces added together.

You have two trapezium faces, 1 rectangle base, and two inclined rectangles.

The area of the trapezium faces => 2 [ 1/2 * ( 8x + 10x ) * x ] = 18x^2

The area of the base => 8x * y => 8x * 100 / x^2 => 800 / x

Now for the last bit, they tell you in the question, the two smaller rectangles are inclined at 45 degrees to the horizontal. With this in mind, you end up with:

The ratios in this triangle are, 1√2, with the 1's belonging to the adjacent and opposite, and √2 for the hypotenuse.

Since x is an opposite, and we're trying to find the hypotenuse ......
that leaves us with x : ? ---> 1 : √2 giving us ? = x√2

The area of the smaller rectangles : 2 (x√2 * y) => 2( x√2 * 100 / x^2 )
= 200x√2 / x^2 = 200√2 / x

Area of metal used => 18x^2 + (800/x) + ( 200√2 / x )

You factorize the two which have x in their denominator to:

18x^2 + 200( 4 + √2 ) / x

Hope any of that made sense....

Thank you! I'm still confused. But thanks.
4. (Original post by frozo123)
I swear you were the one who memorised all the proofs the other day haha
you'll do well chill
maybe because thats the only thing where you dont need a brain to get marks
they never come up anyway

C1 was good...i can smell C2 failure , gotta suck it up and revise though *sigh*
5. What are the proofs we need to know in C2 and the list of the formulae of all the shapes (e.g. volume and SA of cylinder)
6. (Original post by Tiam.N)
What are the proofs we need to know in C2 and the list of the formulae of all the shapes (e.g. volume and SA of cylinder)
just two trig identities
don't bother using any ones that are outside of AS because the question should be done only using those 2
sin^2x +cos^2x=1
tanx=sinx/cosx

then Area of Sector and Length of Arc
Area of a circle
area of a triangle
Prisms cross sectional areax length
so area of trapezium may come in handy

that's it tbf
7. (Original post by ParisInc.)
That's right, can you please explain how you did it?

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Each unit on the axes is 8 across, so a square unit is 8 squared right? which is 64.
You have R number of square units in the cross section so its R x 64. Then you factor in the depth which is 2.

So the final calculation is R x 64 (for the cross sectional area) x 2 (for the depth)
8. (Original post by husband material)

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Nice username, but i am husband material
9. slap this on your wall and memorise it. I pretty much guarantee it will come up!!!
Attached Files
10. Sum of geometric series.docx (52.0 KB, 146 views)
11. (Original post by Ahsen2015)
LOL that is the same question i'm struggling with too, need to go over that
Haha, I sort of gave up. I managed to understand why a is 2, but can't get b yet. But frozo123's post really helped
12. (Original post by danthebox)
slap this on your wall and memorise it. I pretty much guarantee it will come up!!!
Let's hope! They haven't done it for ages and it's easy marks, lol.
13. i done loads of past papers and kept on getting to a proof question and being like wtf haha, anyhow, I've learnt it now so hopefully it comes up lol
14. (Original post by danthebox)
i done loads of past papers and kept on getting to a proof question and being like wtf haha, anyhow, I've learnt it now so hopefully it comes up lol
which proof?
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16. (Original post by laurenjjj)

I dont understand why the (1-r^n) in the sum formula has been changed to (r^n-1) in the mark scheme? Why is this?
It's an alternate form of the formula for Sn. Don't worry about it, it's mainly used when r>1 as specified in this question.
17. (Original post by frozo123)
which proof?
proving the sum of n terms of a geometric series
Haha, I sort of gave up. I managed to understand why a is 2, but can't get b yet. But frozo123's post really helped
Have you got it now? Sub a back into any of the equations
then to understand what you've done
Solve

sin(ax-b)=0 0<x<360 ( the inequality sign meant to be or equal to )

so let (ax-b)= theta

so values are 0, pi, 2pi
you should get what the coordinates are in the question
19. (Original post by danthebox)
proving the sum of n terms of a geometric series
paste it on here I can't remember it cheers
20. (Original post by frozo123)
paste it on here I can't remember it cheers
here
Attached Files
21. Sum of geometric series.docx (52.0 KB, 77 views)
22. So guys, ive summed up my very dumb maths doubts, very simple and quick to answer like weird equations etc, can any one show me a paper work solution of these, if not, one of these? Its hell important, as my basics realllyyy sucks! Please help!
Attached Images
23. MATHS.pdf (353.7 KB, 108 views)

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