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# C3 exponential function watch

1. P = (2800ae^0.2t)/(1+ae^0.2t)

a=0.12

Show that p = 336/(0.12+e^-0.2t)

I get that if you divide by e^0.2t you get the answer, but why do you do this ?

Help much apprieciated, thanks in advance
2. (Original post by style)
P = (2800ae^0.2t)/(1+ae^0.2t)

a=0.12

Show that p = 336/(0.12+e^-0.2t)

I get that if you divide by e^0.2t you get the answer, but why do you do this ?

Help much apprieciated, thanks in advance
Are you asking what the point of the question is? Like, why do they want to express p in that form? Without more context, there doesn't seem to be any sensible reason.
3. I don't understand what you mean You already know what to do, divide through by e^0.2t. The reason you do it is to get the mark...
4. I think the question is whether you're able to apply it so something else after solving it. Obviously not whether you get a mark or not for doing the right thing.

5. (Original post by JoshFlack)
I don't understand what you mean You already know what to do, divide through by e^0.2t. The reason you do it is to get the mark...
It's because thats what I did before a few months ago when I did this question, re doing it now I don't remember the reasoning behind it.
6. (Original post by Swayum)
Are you asking what the point of the question is? Like, why do they want to express p in that form? Without more context, there doesn't seem to be any sensible reason.
No, I was stuck on this question but looking over some previous notes i saw that I divided it by e^0.2t to get the answer. But the thing is I don't remember why I did that, and I can't figure out the reasoning behind it.
7. (Original post by style)
No, I was stuck on this question but looking over some previous notes i saw that I divided it by e^0.2t to get the answer. But the thing is I don't remember why I did that, and I can't figure out the reasoning behind it.
if i remember correctly, part of the question was just getting you to rearrange it. you know like how they do that in numerical methods questions
8. Just forget it, its only worth 1 mark.
Thanks every1
9. (Original post by maxfire)

could you explain the second step please, thanks.
10. (Original post by skk90)
could you explain the second step please, thanks.
Divide the top and the bottom of the fraction by
11. P=(336e^0.2t)/(1+0.12e^0.2t)
then factorise out e^0.2t on the bottom, giving you ((1/e^0.2t)+0.12) you can then cancel out e^02t
then the 1/e^0.2t gives you the e^-0.2t
12. (Original post by maxfire)
Divide the top and the bottom of the fraction by
How did u divide the bottom part of the fraction by it?
13. e^0.2t(1/e^0.2t)+0.12)
you get that
then (1/e^0.2t)+0.12=0.12+e^-0.2t
14. How do I differentiate y= cot x^2 (not cot^2 x)
15. (Original post by skk90)
How do I differentiate y= cot x^2 (not cot^2 x)
Use the chain rule: the derivative of f(g(x)) is g'(x) f '(g(x)).

[The derivative of cot x is -cosec^2 x].
16. (Original post by meatball893)
Use the chain rule: the derivative of f(g(x)) is g'(x) f '(g(x)).

[The derivative of cot x is -cosec^2 x].
Why isn't the g'(x) multiplied by f ?
17. (Original post by skk90)
How do I differentiate y= cot x^2 (not cot^2 x)
in order to differentiate cotf(x) you use: -f'(x)cosec2f(x)

therefore, the answer would be: -2xcosex2x2
18. (Original post by skk90)
How do I differentiate y= cot x^2 (not cot^2 x)
if im not wrong its: -2cotxcosec^2.x using the chain rule on (cotx)^2 leting u=cotx and y=u^2
19. (Original post by amzy2)
if im not wrong its: -2cotxcosec^2.x
how come? I'm pretty sure it's -2xcosec2x2.

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