Edexcel C3,C4 June 2013 Thread

Reply 4540

Giant

11

Original post by Jullith

Still need help with part c of this:

C4 4.png

And part c of this:
(I'm confused as to what the limits are)

C4 3.JPG

Help would be appreciated, thanks!

For the second one, it says the finite region of the curve bounded by x=5/2. So the limits would be 5/2 and 1 in terms of x. You need to convert them to in terms of t if you are integrating parametrically.

Reply 4541

Chris-69

7

Original post by fayled

Change of base formula.

log₁₀x=lnx/ln10

Didn't spot that, thank you!

Reply 4542

fayled

9

Original post by KD35

Lets set ourselves some hard questions guys!

Integrate 4^(2x^2)

Thats 4 to the power 2x^2

Do you know the answer yourself?

Reply 4543

Jullith

Original post by Giant

For the second one, it says the finite region of the curve bounded by x=5/2. So the limits would be 5/2 and 1 in terms of x. You need to convert them to in terms of t if you are integrating parametrically.

I tried converting the limit from x to t but it didn't work for x=1, since you get t^(2)-t+1 which can't be factorised?

Reply 4544

Matamaticas

2

Anyone else feeling worn out just by the thought of doing this replacement paper tomorrow? :rolleyes:

Reply 4545

KD35

15

Original post by Zaphod77

Is it just the x squared, or the 2x all squared?

Original post by fayled

Do you know the answer yourself?

Just the x and yes I think I do

Reply 4546

Zazuwaved

10

Original post by Matamaticas

Anyone else feeling worn out just by the thought of doing this replacement paper tomorrow? :rolleyes:

Really worn out, seriously don't know what to expect. Main aim: try and get as many method marks here and there as possible.

Reply 4547

Ohmydog

7

Original post by KD35

Lets set ourselves some hard questions guys!

Integrate 4^(2x^2)

Thats 4 to the power 2x^2

4^(2x^2)ln(4)4x??
edit: oops, no wrong. I thought you said differentiate!

Reply 4548

justinawe

19

Original post by KD35

Lets set ourselves some hard questions guys!

Integrate 4^(2x^2)

Thats 4 to the power 2x^2

Try not to make up questions just like that, the answer has to be attainable with C4 knowledge.

http://www.wolframalpha.com/input/?i=integral&a=*C.integral-_*Calculator.dflt-&f2=4^%282x^2%29&x=10&y=13&f=Integral.integrand_4^%282x^2%29&a=*FVarOpt.1-_**-.***Integral.rangestart-.*Integral.rangeend--.**Integral.variable---.*--

Definitely not C4 stuff, that.

Reply 4549

wndms

1

Can someone help me with 8b)?
So firstly I equated sin4t=0 to get x values. But I got 4 solutions? What? I didnt know what to do after... thanks

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Reply 4550

kuku2013

Original post by justinawe

For 2^x, yes.

In general,

\dfrac{d}{dx}(a^x) = a^x \ln a

\displaystyle \int a^x \ dx = \dfrac{a^x}{\ln a} + C

are there any other uncommon one's I should know about. cause this I couldn't do I the jan 2013 and made me miss my a* by 1 mark

Reply 4551

Story

Original post by Zaphod77

No problem, happy to help :smile:

If its not too much to ask, do you have any tips on some stuff like integration, some of the stuff I fumble on, like substitution.

Also if you had x^3/2, For some reason I thought that would cancel down as square roots and power cancel each other, I know they do not but why?

Also on differential equations I dont know if you have done the past paper or not but june 2012 c4 q)4) It says solve the differential equation dy/dx =3/ycos^2x ... My question is the ms did not move the 3 however I did and I managed to get y^2 = 6tanx (the same answer on ms) would this be awarded the same and are there any major rules when separating differential equation ie, what you CANT do?

Reply 4552

silentriver

Original post by imasha.sj

Hey guys!

Can someone help me with Edexcel C4 review exercise question 74 (c)? I don't get why we have to integrate from 0.5 to 2....Thanks in advance :smile:

from the earlier part of the question, we find that when x=2.5 , t=0.5 and t=2. In part c we have to integrate in terms of t, not x. therefore once you intergrate using (y.dx/dt) you can simply put in the t values as the limits and get your answer! I had a confusion in this question too! But instead of using the x values, we can use the t values,either way, you will get the the region enclosed with curve.. hope this helps.

Reply 4553

yaboy

Anyone understand why there is different answers in question 8a june 2008???

When I sub the x value in I get t=pi/3 and when I sub the y value in I get t= pi/6

Reply 4554

sonyeric33

1

Original post by KD35

Lets set ourselves some hard questions guys!

Integrate 4^(2x^2)

Thats 4 to the power 2x^2

i dunno if correct but is it

4^(2(X)^2) / 4X * Ln 4?

Reply 4555

Kreayshawn

why can't the cartesian equation be x = ln(root[y+2])
for part b?
correct answer is
y = e^2x - 2

Reply 4556

Zaphod77

1

Original post by Story

If its not too much to ask, do you have any tips on some stuff like integration, some of the stuff I fumble on, like substitution.

Also if you had x^3/2, For some reason I thought that would cancel down as square roots and power cancel each other, I know they do not but why?

Also on differential equations I dont know if you have done the past paper or not but june 2012 c4 q)4) It says solve the differential equation dy/dx =3/ycos^2x ... My question is the ms did not move the 3 however I did and I managed to get y^2 = 6tanx (the same answer on ms) would this be awarded the same and are there any major rules when separating differential equation ie, what you CANT do?

With regards to substitution, use the steps I said earlier. Never forget to change the limits, and if one substitution isn't working for you and they didn't specify the substitution you should use, try another - they'll all work out the same in the end. Only use substitution when you have a function of a function! Your second question, the power 3/2 means you square root a number and then cube it. If you had 4^3/2 you would square root it (2) and then cube it (8). If you had x^3/2 you could write it as root(x) * root(x) * root(x), which would then be the same as xroot(x) if you like :smile:

With regards to your 3rd question, it doesn't matter at all. They only did it like that in the mark scheme because it involves less steps, but it doesn't matter so long as you get to the right answer :smile: