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# Edexcel A2 C4 Mathematics June 2016 - Official Thread watch

Isn't that from the IAL paper? that trig application question?
Yep, the june 2014 c34 paper, q13(b)
I get the rest of the question and what they're trying to do but I cant seem to see why those two angles are the same
2. Guys I have a quick qs on C34 june 2014 IAL : aka Zacken

Qs. 6b if we're finding a general solution for a differential equation, why does it matter if I sub in boundary conditions in y = f(x) form to find C instead of leaving it in ln form?

You see if I leave it in y form and find C I get 35/9, but the mark scheme solved C in ln form and got ln(36) Ultimately the final answer aka the y=f(x) form for the particular solution is different...

my answer = y = (2x-1) / (x+1)^3 + 35/9

mark scheme = y = 36(2x-1) / (x+1)^3

Can someone explain why I need to leave it in ln form to find C and why it affects the final answer thanks. Appreciate it! x
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3. I've never really understood why when they say that 'the tangent to the curve at Q is parallel to the y-axis.'. you have to make the denominator equal to zero. (this is after you have found dy/dx).

Can someone please explain to me why this is so because i just cant seem to visualise it. Thanks
4. (Original post by Lilly1234567890)
I've never really understood why when they say that 'the tangent to the curve at Q is parallel to the y-axis.'. you have to make the denominator equal to zero. (this is after you have found dy/dx).

Can someone please explain to me why this is so because i just cant seem to visualise it. Thanks
Haven't really thought about it before in the terms you describe, but the reason is that a line parallel to the y-axis has an infinite gradient, and this is the same as dividing by 0 (it also means that the normal has 0 gradient)
hope this helps
5. (Original post by Lilly1234567890)
I've never really understood why when they say that 'the tangent to the curve at Q is parallel to the y-axis.'. you have to make the denominator equal to zero. (this is after you have found dy/dx).

Can someone please explain to me why this is so because i just cant seem to visualise it. Thanks
If tangent is paralel to y it means the gradient is straight up...so dy/dx has to equal infinite, in fractions x/0 equals infintie
6. (Original post by ryandaniels2015)
Crash course of vectors!

A little might be missed out but enough to get started on Past papers!
Thank you!!
7. (Original post by zarzaidi)
Guys I have a quick qs on C34 june 2014 IAL : aka Zacken

Qs. 6b if we're finding a general solution for a differential equation, why does it matter if I sub in boundary conditions in y = f(x) form to find C instead of leaving it in ln form?

You see if I leave it in y form and find C I get 35/9, but the mark scheme solved C in ln form and got ln(36) Ultimately the final answer aka the y=f(x) form for the particular solution is different...

my answer = y = (2x-1) / (x+1)^3 + 35/9

mark scheme = y = 36(2x-1) / (x+1)^3

Can someone explain why I need to leave it in ln form to find C and why it affects the final answer thanks. Appreciate it! x
I'm not sure, but are you 100% sure that you've done it right for your method?
8. SeanFM Do you have a solid method for answering questions like part bii of this?

9. (Original post by Don Pedro K.)
SeanFM Do you have a solid method for answering questions like part bii of this?

Nothing really special.. just find where sin(theta-alpha) = 1, (pay attention to the range) that's where the maximum will be.
10. (Original post by SeanFM)
Nothing really special.. just find where sin(theta-alpha) = 1, (pay attention to the range) that's where the maximum will be.
Ah okay, thanks What do you mean by pay attention the range?
11. (Original post by Don Pedro K.)
Ah okay, thanks What do you mean by pay attention the range?
Choose the right value of theta then you're solving sinx = 1 where x = theta - alpha.
12. (Original post by SeanFM)
Choose the right value of theta then you're solving sinx = 1 where x = theta - alpha.
Oh okay so using 2theta etc. when the question had (2theta - a)?
13. (Original post by Don Pedro K.)
Oh okay so using 2theta etc. when the question had (2theta - a)?
Just stuff like that when you're trying to solve trig equations, yes.
14. (Original post by SeanFM)
Just stuff like that when you're trying to solve trig equations, yes.
Okay, danke
15. (Original post by philo-jitsu)
If tangent is paralel to y it means the gradient is straight up...so dy/dx has to equal infinite, in fractions x/0 equals infintie
(Original post by candol)
Haven't really thought about it before in the terms you describe, but the reason is that a line parallel to the y-axis has an infinite gradient, and this is the same as dividing by 0 (it also means that the normal has 0 gradient)
hope this helps
Thanks ! what if they said that the tangent is parallel to the x-axis. that's infinite as well. so surely we must equal the numerator to zero right?
16. (Original post by Lilly1234567890)
Thanks ! what if they said that the tangent is parallel to the x-axis. that's infinite as well. so surely we must equal the numerator to zero right?
17. (Original post by SeanFM)
I'm not sure, but are you 100% sure that you've done it right for your method?

Hey, thanks for the reply. Yeah I'm pretty sure my method is right, my steps conform to the mark scheme up until they keep it in ln form and I apply e and arrange in y=f(x) form but we still get different values for C which I don't get.

18. Can someone help me with this question
June 2011 q6)d

I got the answer wrong because I put line 1 as line 2 and line 2 as line 1 so used tan when I was meant to use sin. Can someone tell me how to chose the right one for exam

QP
https://a086a5a2f39bda93734c56a63fab...%20Edexcel.pdf

MS
https://a086a5a2f39bda93734c56a63fab...%20Edexcel.pdf

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19. (Original post by candol)
Connected rates of change are often similar types of question. Ideas include:
Think what the 3 differentials in your equation must be
Think what basic shape info you need to create your missing differential

Please put up a question you don't like for us to look at
Thanks for helping! Heres an example (part b):

20. (Original post by lordoftheties)
Thanks for helping! Heres an example (part b):

How do you do part (a) to that question?

V = 1/3 . pi . r^2 . h

do you divide the r/h = 16/24 = 2/3

Can't remember.

Where did you get that question from?

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