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Edexcel A2 C4 Mathematics June 2016 - Official Thread watch

1. (Original post by Craig1998)
30+50e^0.002t> 84
50e^0.002t>54
e^0.002t>27/25
t/500>ln1.08
t>500ln1.08
t>38.4

Therefore t = 39
Therefore year = 1980+39
= 2019.

Oh god I'm failing c4.
That's correct
2. (Original post by Craig1998)
30+50e^0.002t> 84
50e^0.002t>54
e^0.002t>27/25
t/500>ln1.08
t>500ln1.08
t>38.4

Therefore t = 39
Therefore year = 1980+39
= 2019.

Oh god I'm failing c4.
Yep thats what I got, but the mark scheme says 2018, must be an error on their part.

Btw this is C3 , im sure you'll be fine. Thanks!
3. Q) Why is the gradient of tangent --> 1/(value of dy/dx)

when https://gyazo.com/1cd6bd9ac94dbec89e08132a94ff86a1
shows the gradient of tangent is the exact value of dy/dx yet this shows the gradient of tangent
is https://gyazo.com/a31c58f4855ac1c0d1d8b6177b8a08a2 .

I understand when you draw a picture you can see gradient of tangent is 1/gradient but say for example
if they say ' find the equation of tangent of the line. ' then the tangent 'm' value in the equation would be
the dy/dx value and if they ask 'find the equation of tangent TO A PARTICULAR POINT' then do you do 1/gradient. <--- is that right?

I don't know why this has confused me last minute
4. wot. Gradient of tangent is dy/dx.
5. (Original post by Zacken)
wot. Gradient of tangent is dy/dx.
That's what I thought. I was confused by what that person did in that workings.

Can you explain this to me please.

Question: https://gyazo.com/dbdd9ce6a296f8c337e633e69cd442b3

I got that 1st line in the mark scheme where I dy/dx: 3sqroot(2) . cos (theta+ alpha)

and dy/dx = 1/2 so why can't I do 3sqroot(2) . cos(theta+alpha) = 1/2?

How did they get -2 or 2? Is it from the graph or something I missed?
6. (Original post by XxKingSniprxX)
...
...you could have given us the question in the first place.

This is of the form x = f(y). So the gradient of the tangent is given by dx/dy.

In most questions, the curve is defined as y = f(x) so the gradient of the tangent is dy/dx.

In the question you've linked, you've found x = f(y), so by differentiating you get dx/dy = f ' (y).

You want dy/dx. So dx/dy = 1/(dy/dx).
7. (Original post by Zacken)
...you could have given us the question in the first place.

This is of the form x = f(y). So the gradient of the tangent is given by dx/dy.

In most questions, the curve is defined as y = f(x) so the gradient of the tangent is dy/dx.

In the question you've linked, you've found x = f(y), so by differentiating you get dx/dy = f ' (y).

You want dy/dx. So dx/dy = 1/(dy/dx).
I've been reading the question as y = f(x) ---> L

Thanks, I understood it easy once I realised it was x = f(y)
8. (Original post by XxKingSniprxX)
I've been reading the question as y = f(x) ---> L

Thanks, I understood it easy once I realised it was x = f(y)
Coolio.
9. (Original post by XxKingSniprxX)
Q) Why is the gradient of tangent --> 1/(value of dy/dx)

when https://gyazo.com/1cd6bd9ac94dbec89e08132a94ff86a1
shows the gradient of tangent is the exact value of dy/dx yet this shows the gradient of tangent
is https://gyazo.com/a31c58f4855ac1c0d1d8b6177b8a08a2 .

I understand when you draw a picture you can see gradient of tangent is 1/gradient but say for example
if they say ' find the equation of tangent of the line. ' then the tangent 'm' value in the equation would be
the dy/dx value and if they ask 'find the equation of tangent TO A PARTICULAR POINT' then do you do 1/gradient. <--- is that right?

I don't know why this has confused me last minute
I would expect someone getting 95+ to not be thrown off by this of all things.
10. (Original post by yesyesyesno)
I would expect someone getting 95+ to not be thrown off by this of all things.
Haha.. we all have our moments.
11. anyone have the AQA C3 paper? ive heard it was a beast of a paper. I wanna see how hard it really was
12. How do I go from my alternative answer to getting the quadratic equation they formed in this question?

https://gyazo.com/861095830fbde070b20076a796aeba94
13. (Original post by XxKingSniprxX)
How do I go from my alternative answer to getting the quadratic equation they formed in this question?

https://gyazo.com/861095830fbde070b20076a796aeba94
That's how you do it. But to be honest I don't know why your way won't work. Always hated that about logs. For some reason I can only get one way to work. Rest give me wrong answers even if they seem right.

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14. (Original post by XxKingSniprxX)
How do I go from my alternative answer to getting the quadratic equation they formed in this question?

https://gyazo.com/861095830fbde070b20076a796aeba94
You can't antilog like that, you have to use the log rule, from C2: -log(x) is log(1/x)

Once you've both logs on the side, you can anti-log it.
You can't antilog like that, you have to use the log rule, from C2: -log(x) is log(1/x)

Once you've both logs on the side, you can anti-log it.
Do you mind explaining further please. I don't understand. I get how to do it but I don't get why the way he did it first doesn't work. Please and thanks.

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16. (Original post by ImNervous)
Do you mind explaining further please. I don't understand. I get how to do it but I don't get why the way he did it first doesn't work. Please and thanks.

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You can just anti log from the 1st line since its already in logs. Your way is much more working out involved.

You can't antilog like that, you have to use the log rule, from C2: -log(x) is log(1/x)

Once you've both logs on the side, you can anti-log it.
--> I can't believe I'm forgetting basic maths. :L

17. (Original post by XxKingSniprxX)
You can just anti log from the 1st line since its already in logs. Your way is much more working out involved.

--> I can't believe I'm forgetting basic maths. :L

Ooh wow. I'm an idiot. Lol

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18. Who else almost made vectors their b*tch here?

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19. (Original post by ImNervous)
Ooh wow. I'm an idiot. Lol

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at the stupid maths mistakes.
20. (Original post by кяя)
Who else almost made vectors their b*tch here?

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Vectors is my b*tch now ;D

(Original post by XxKingSniprxX)
at the stupid maths mistakes.
These silly arithmetic mistakes always get you and you lose free marks, costed me my 200 UMS in C12 >.<

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