Edexcel A2 C4 Mathematics June 2016 - Official Thread

I am not worried about A* I am just trying my best to get a B :P

Reply 3202

Yua

14

anyone else tend to make a lot of mistakes in c4?

Reply 3203

Someboady

17

Original post by Yua

anyone else tend to make a lot of mistakes in c4?

Yes I am prone to errors in C4. Very simple things really but I just need to take my time a bit i think. Idk what else i can do except papers to revise xD

Does anyone have some difficult Differential Equation questions?

Reply 3204

BrainJuice

15

Do we need to know how to derive the differentiation of y = a^x

Reply 3205

skeptical_john

13

Original post by BrainJuice

Do we need to know how to derive the differentiation of y = a^x

My revision book says we need to but I've seen it come up in past papers (not done that many tho)

Reply 3206

Original post by BrainJuice

Do we need to know how to derive the differentiation of y = a^x

I don't think we need to know how to derive it, but it's not too difficult anyway

y = a^x
lny = lna^x
lny = xln(a)
x = lny/lna (lna is a constant here)
dx/dy = 1/yln(a)
dy/dx = yln(a)
dy/dx = a^xln(a)

Something like this

Reply 3207

tommyprice5

Original post by BrainJuice

Do we need to know how to derive the differentiation of y = a^x

It's really not that hard, if you look at the C3 formula sheet you can see that a^x=e^(xlna), then differentiate it in this form (giving lnae^(xlna)) and change e^(xlna) back to a^x

Reply 3208

When integrating by parts does anyone have a list or any tips or rules on which part should be u and which part should be dv/dx? I think I saw a helpful list online somewhere that recommended the right way for lots of examples

Reply 3209

NotNotBatman

20

Original post by Yua

anyone else tend to make a lot of mistakes in c4?

yes, this morning I did a gold paper.
- I wrote two cubed terms in the binomial expansion; accidentally writing the squared term as a cube.
- copied down dx/dt wrong when writing dy/dx. 4sint, instead of 4sin2t
- did something wrong in part (b)

If we are trying to find angle ACB aren't you supposed to use vectors CA and CB rather than AC and BC?

and I need 100% :frown:

Reply 3210

Yua

14

Original post by NotNotBatman

yes, this morning I did a gold paper.
- I wrote two cubed terms in the binomial expansion; accidentally writing the squared term as a cube.
- copied down dx/dt wrong when writing dy/dx. 4sint, instead of 4sin2t
- did something wrong in part (b)

If we are trying to find angle ACB aren't you supposed to use vectors CA and CB rather than AC and BC?

and I need 100% :frown:

Same here, silly mistakes in binomials and integration - missing a negative sign and such

No you would AC and BC, you need the vectors moving away from the angle not towards it

Reply 3211

Kevin De Bruyne

21

Original post by Ainsleyy

When integrating by parts does anyone have a list or any tips or rules on which part should be u and which part should be dv/dx? I think I saw a helpful list online somewhere that recommended the right way for lots of examples

I'm sure stuff like that exists, but I would say, before integrating at all, look at which one would simplify or make the integral look nicer, so kind of plan it in your head if you want to look at it that way. This could be like seeing x differentiating to 1 so that you're integrating 1 * something else, or choosing to differentiate x^2 in x^2e^x^2 so that you're integrating 2xe^x^2 etc.

Reply 3212

Original post by Yua

Same here, silly mistakes in binomials and integration - missing a negative sign and such

No you would AC and BC, you need the vectors moving away from the angle not towards it

AC and BC go towards C dont they? Or am I going crazy

Reply 3213

Original post by Ainsleyy

When integrating by parts does anyone have a list or any tips or rules on which part should be u and which part should be dv/dx? I think I saw a helpful list online somewhere that recommended the right way for lots of examples

My teacher said use this order of preference for the u part that you differentiate:

(n is any integer)
lnx > x^n > e^x + trig functions

lnx you can't integrate so you have to do it by parts and differentiate it

Reply 3214

NotNotBatman

20

Original post by Ainsleyy

AC and BC go towards C dont they? Or am I going crazy

Original post by Yua

Same here, silly mistakes in binomials and integration - missing a negative sign and such

No you would AC and BC, you need the vectors moving away from the angle not towards it

Just checked you do need CA and CB, although the mark scheme finds AC and BC for some reason, I just did
-5-(-1)=4 so I got the vector CB wrong.

Reply 3215

Original post by NotNotBatman

Just checked you do need CA and CB, although the mark scheme finds AC and BC for some reason, I just did
-5-(-1)=4 so I got the vector CB wrong.

Surely it doesn't matter which set you get? AC and BC will give the opposite sign to CA and CB but when you calculate the angle you do cos(theta) = |blah| so it's positive anyway?

Reply 3216

Original post by Swifty139

My teacher said use this order of preference for the u part that you differentiate:

(n is any integer)
lnx > x^n > e^x + trig functions

lnx you can't integrate so you have to do it by parts and differentiate it

Thanks alot man thats very helpful

Reply 3217

Guys do we need to know how to integrate by substitution without them telling us what u is? e.g integrate (sinx)^5(cosx)

Reply 3218