Edexcel C3,C4 June 2013 Thread

If two vectors are perpendicular to each other they have a right angle between them i.e. 90 degree or pi/2. Cosine is 0 at 90 degree.
therefore some unknown vector of
x,y,z . 2i+j-k =0
and
x, y, z . i+j-2k = 0

Dot the vector xi+yj+zk with each of the others, making the dot product equal to 0. This gives you 2 equations with 3 unknowns. Choose any value for one of the variables, say x=1, then work out the corresponding values of y and z. The reason that you have a choice is that the vector can have any length you like.

When you say that your answer is wrong, is it a multiple of what you think the answer is? If so, your answer is right.

Still not sure what you mean

I don't understand how you can solve 3 Unknown Variables with only 2 Simultaneous Equations.

Don't know what you me choose a value for any of the variables? - Please could you care to explain?

On a positive note finished the End of Chapter Questions now...I can see why I was no where near A* Material in January. Such an Epic Amateur I am. Think I'm ready for C4 Solomon Press Papers now....let's do this!

Let z=1 or whatever value. And then solve x and y when z =1 there are infinite vectors that can be perpendicular to those two. Imagine to lines in the space. You can draw infinite lines that are perpendicular to those two lines.

Boom I see your logic - what I didn't understand before is that there could be so many Perpendicular Vectors to Two Lines. I'm guessing that would imply that they are not skew or rather must intersect... a bit difficult to visualize.

And cheers and bro! You replied at the perfect time

And take your imagination further.
These two vectors can go from one end of the universe to the other end of the universe and therefore many perpendicular lines. And yes No they don't have to intersect to be perpendicular. As long as the lines are drawn correctly it would be perpendicular.

You just need a bit of imagination in vectors.
Or just draw it 2d on a paper.

Thanks so much man. Speaking to you has been really really great.

Just the way you think about things. I'm realizing getting good marks isn't just about some score on a piece of paper - it is but it is the sum of you really have to push yourself to think over a long period of time.

That analogy you just made is going to help me so so much when I do Physics questions.

I am so used to just looking in the back of the book, and its taking a real learning curve to just stop myself, and work through it!!

Dan is my official studentroom Hero.

I'm becoming increasingly worried about my C3 resit and C4 this June. I'm focusing on other modules this week but I'll have a look at those two next week.

Foolish of me to not have done the Zigzag papers because I though they wouldn't ask questions like that... what did you get in C3/C4??

Not you Qwetry as long as you do better, heads up past papers in! I got a B. No sweat, Keep Calm and Past Paper On.

I am just wondering about what Masmammad got, and if the ZigZag meant he got like 100UMS or something.

I'm becoming increasingly worried about my C3 resit and C4 this June. I'm focusing on other modules this week but I'll have a look at those two next week.

i did both this jan i got 98 for c3 and 99 for c4. tbh i wish all the modules were pure, cuz you know what to do with pure. do papers and learn from your mistakes and you'll be fine.

Boom!

Yeah this is what I'm talking about, good students all do the same thing, loads of questions and just learn from mistakes as you go along.

Yeah cheers mate, if I have time I will try to do the Zig-Zag Papers then like by the end of April or something.

There are alot of Solomon Press though - 12 Solomon Press, and according to what you said 5 Zig-Zag for both C3 and C4

Not so sure how I will fit this in carefully.

Think I will only do 2009-2012 for the real papers.

How many do you think I should aim to do for each????/

I'm not too worried. I am going through Solomon Press under timed conditions and realising I had alot of Weaknesses. Surprised I was even able to pull of a High B.

I've only done C4 and C3 Paper A but already identified my Vectors was weak, which I have done all the End of Chapter Questions for, and my Integration is just dire for C4.

I think I've lost around 20 marks on integration on C4 A. Just did it now 1hr30 mins was painful.

But I'm just glad that I was able to get a B despite being so weak at the subject. It means if I finish all Solomon Press this April for C3 and C4 then do all past papers in May I should be able to get an A*.

Thank god for some high caliber students on this forum who help out. I was working completely wrong before. Your supposed to be just reducing all your weaknesses until your on an A* for each topic they throw at you.

I was a big amateur.

P.S I copied your sig muhhahaha it will make it easy for me to see my exams

I'm definitely going to do Solomon. I was getting 95+% in C3 past past papers. As you can imagine I was extreemly dissapointed with my result.

can someone help me?
I want to integrate:
$\int cos^2x dx$

I did:
using $cos2A$ identity; $2cos^2A-1 => 2cos^2A=cos2A+1$
$cos^2A=1/2(cos2A+1)$
now $\int 1/2(cos2x-1) dx =>(1/2)[(1/2)(sin2x+1)]+c$
$1/4sin2x+1/2+c$? Is this right?

nope you have to treat cos2x + 1 as 2 different entities not 1, you do intergral of 1/2 cos2x which is 1/4sin2x and then integrate +1/2 which is +1/2 x

You get 1/4 sin2x + 1/2x +c (i think)

If I was you I would take the 1/2 outside the integral sign to make it simple and just integrate cos2x+1 as normal and bring it back right at the end

x

I don't understand this question: $\int (1+sinx)^2$
here's what i did: $(1+sinx)(1+sinx)=1+2sinx+sin^2x=cos^2x+2sinx?$ (am i on the right lines?)