WJEC C4 June 2011

How did you all find it ?

These are my answers..

1 a) -3/ (x+2) ^2 + 1 / (x+3)

b)0.246

2a) Gradient was 2, gradinet of normal was -1/2.
Equation was 2y + x =7

3a) 0, 180, 35.26, 215.26

b) 50.21, 309.79, 25.53, 123.95

4 a) Show the tangent...

5a) Coordinates

b) i had 18 pi

6) 1 - 6x+ 27x^2

7a) forogt

b) 0.24

8 a) dn/dt = kn

b) A is e^c

c) When t=20. N=233

9a) 7

9b) Mew = -3.2
Landa= 0.4

10 (3x-2)^2 < 0

Same answers?

Scroll to see replies

Reply 1

Pronitron

Hi, I agree with your 1 a) + 1 b) 2(a), one of your 3a) values is wrong as it asks for values between 0 and 180, you wanted 144.73 I think as arctan(-1/?2) gives that value, the coordinates for 4 were (2?3,0) and (0,8), your value for 5(b) is half the true value, it should be 36 pi, you're meant to test your answer in the second part by doing 4/3*pi*r^3 i.e the volume of a sphere and with radius 3 that works out as 36 pi, so does ?9-x^2 dx between -3 and 3 times pi. (6) I got 3+10x-29x^2 which is correct according to wolfram alpha and absolute value less than 1/3rd, (b) is correct, so is (8), 9(a) is correct and for (9b) i got lambda = 1 and mu = -3 I think as my k parameter worked out as -4=-5 showing no interesection, (10) I can't remember the quadratic but I think I got (2x-3)^2 meaning x=3/2 not 2/3 like you have, which would be 4x+9/x<12, pretty sure that was it wasn't it? Anyway good luck :smile:

Reply 2

Pronitron

Those question marks were an integral sign and a sqrt sign btw :P

Reply 3

tom108

Original post by Pronitron

You know 8b) Did you have N = e^3 + e^kt

And sorry i meant what you said in 10.

Did you get the same value as me in 3b?

For 5bi) I did the range of values between 0 and 3. HOw many marks would i have lost?

Now for the vectors one. My teacher said that i was right with them values. I have the paper here. I will work it out again. haha

Reply 4

Pronitron

(8b) I took logs so I had ln(100)=ln(A)+2k and ln(160)=ln(A)+12k and solve it that way, with 3b I only got two values arcos(16/25) gets you 50.21 and also 309.79, but you seem to have forgotten to add ? at the end, which was 73.74, so you notice that you can't count the 309.79 as it + ? >360 so there's another value as cos(x)=cos(-x) so -50.21 degrees and 50.21 degrees are what you want, you then add ? on to them to get 123.95 and 23.53 so two of your answers are correct and because the graph has shifted two of your answers are not :P, not sure if they'll mark you wrong for that, how do you mean the range, you integrated between 0 and 3?? I guess you might lose 1 or 2, it's not a giant big deal, I think you needed to mention volume of a sphere is 4/3*pi*r^3 for the second bit though. Okay, three of my friends got the same answers for the vector one but sure :P Any chance you could scan the paper as I would like to check a few things :smile:

Hope this helps.

Reply 5

Pronitron

And the question mark is alpha -_-

Reply 6

tom108

In question 8 did you work out A to be 91.028 then i assume ?
Bit confused about what your saying about 3b, I got all them 4 answers.
You did get 0.24 for 7b did you?
For the vectors one, people were saying it was you say and what i say, so who knows!! haha
Yeah I wil scan it in in school tomorrow. Dont have a scanner at home. :smile:

Reply 7

Pronitron

A was 100/e^(2k) which is approximately 91.028 . Yeh I'm saying you're not meant to count two of them answers, because you're working out values for x-73.74 so that means values between -73.74 and 286.26 initially, after finding those, you add 73.74 to your answers, so the higher one is not between those values so you wouldn't count it, you get me? 50.21, 309.79, 25.53, 123.95 are your answers, 309.79 isn't an answer because when you add 73.74 to it, it's not between 0 and 360, and 50.21 is only a solution for cos(x-73.74), the 123.95 is the correct answer i.e 50.21+73.74 so you should have only two answers, those are 123.95 and 25.53. Yes I got 6/25 which is 0.24. Okay that'd be great, thanks :smile:

Reply 8

tom108

Original post by Pronitron

Ok cheers man. Miight have lost one there then.
Good luck!

Reply 9

hsmith7

Wow you've just made me feel so much better :biggrin:

thought I'd totally screwed up this paper. I have many of the same answers as both of you but I'm going to list them all anyway.

1.a) -3/(x+2)^2 +1/(x-3)
b) 0.246 (3dp)

2. gr of normal = -1/2
equation y-3=-1/2(x-1)

3.a) okay i messed this up :/
b) 25cos($-73.74)
23.53' or 123.95' $= theta

4.a) show equation
b)i) A(2root3, 0) B(0,8)
ii) show length

5.a) okay I've got this question different too...
A(-3,0) B(3,0) C(0,3)
b)i)162pi = 508.94 (2dp) :/
ii) what?

6. 3 + 2x -29x^2 +... Valid for |x|< 1/3

7.a) -x/2.cos(2x) + sin(2x)/ 4 + c

8.a) dn/dt = kn
b)show equation .. i used t= 0 and n=A so work out c and get the equation
c)i) show k
ii)233.031 (3dp)

9.a) a=7
b)i) r=8i +3j -7k + landa ( 2i +j +2k) ???
ii) can't rember what i got landa and mu as but got lhs as -4 and rhs as -5 therefore don't intersect

10. (2x-3)^2 <0 contradiction etc

Right hope this helps :smile:

Reply 10

Pronitron

Here is the expansion around x=0 (i.e binomial) if that helps http://www.wolframalpha.com/input/?i=4%281%2B2x%29^%281%2F2%29-1%2F%281%2B3x%29^2

Reply 11

heartskippedabeat

Original post by hsmith7

Wow you've just made me feel so much better :biggrin:

thought I'd totally screwed up this paper. I have many of the same answers as both of you but I'm going to list them all anyway.

I got most of the same answers as you :yep:

Reply 12

x_Melissa_x

I think I may have got about 40. What do you think that would in terms of grades?

Reply 13

x_Melissa_x

Original post by Pronitron

Yeh I'm saying you're not meant to count two of them answers, because you're working out values for x-73.74 so that means values between -73.74 and 286.26 initially, after finding those, you add 73.74 to your answers, so the higher one is not between those values so you wouldn't count it, you get me? 50.21, 309.79, 25.53, 123.95 are your answers, 309.79 isn't an answer because when you add 73.74 to it, it's not between 0 and 360, and 50.21 is only a solution for cos(x-73.74), the 123.95 is the correct answer i.e 50.21+73.74 so you should have only two answers, those are 123.95 and 25.53. Yes I got 6/25 which is 0.24. Okay that'd be great, thanks :smile:

Wow, I'm not great at maths but I agree with everything you've said! :smile:

Reply 14

Pronitron

Original post by scaddaboosh

i messed up this exam so badly :frown:

had like 9/1800 for intergration by substitution and got like 36pi for 5b) and got horrible factions for question 7.

oh and question 3)

i got it down to tanx (2tan^2x -1) = 0

so tanx = 0 and tan^2x = 1/2
i can get values for tanx = 0 but how do you find values for tan^2x, i tried squaring my final answer but got 700, something (obviously wrong)

36 pi is correct, there are two ways you can do this just to check, integrate x^2-9 between -3 and 3 times pi, or do the volume of a sphere which from GCSE is 4/3 pi r^3, and the radius is 3 so either way you're gonna get 36 pi :smile:

And you'd take the square root of both sides, so you have arctan(±1/sqrt2) :smile:

Reply 15

x_Melissa_x

Original post by scaddaboosh

probably a D, as thats 53% and D range is usually 50-60 UMS

but everyone i know found the paper stupidly hard, and a lot harder than last year, so they might bring the boundaries down, hopefully anyway :smile:

Ah a D would be great :smile:

Reply 16

Pronitron

Sorry I mean 9-x^2 :/

Reply 17

mmeiger

Same answers as you all seem to have as well apart from 3.a I messed up, 5.b.i. 36 pi, ii. didn't attempt and 7.b -0.96.

Reply 18

heartskippedabeat

What did everyone put for the volumes of revolution question , 'evaluate your answer geometrically' or whatever it said?
I had no idea, in the end I just put the object would be a sphere :facepalm2:

Reply 19

scaddaboosh

Original post by Pronitron

And you'd take the square root of both sides, so you have arctan(±1/sqrt2) :smile:

taking the square root makes sense, i messed up some of the exam though, making stupid mistake here and there which costs like 3/4 marks, i need a low B to get an A overall, so i might just do it, fingers crossed