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# C3 - Parametric Equations - Help Watch

1. Here is the question, I don't know why but I don't understand this chapter, if anyone can solve this with working, it would be greatly appreciated.
Thanks
2. (Original post by BroodiestPear)

Here is the question, I don't know why but I don't understand this chapter, if anyone can solve this with working, it would be greatly appreciated.
Thanks
So first you would need to create the cartesian equation, so that's y=...
You can do this a numbers of ways but I usually do it by rearranging one equation to get t=... and substituting the value for t in to the other equation so you're dealing solely with x and ys. From there you can then rearrange to make y=... and then differentiate
3. for part a) you divide dy/dt by dx/dt
4. (Original post by BroodiestPear)

Here is the question, I don't know why but I don't understand this chapter, if anyone can solve this with working, it would be greatly appreciated.
Thanks
Find dx/dt (and hence dt/dx) and dy/dt
Then dy/dx = dy/dt x dt/dx

Posted from TSR Mobile
5. dy/dt = 6 sec^2(t); dx/dt = 3(2cost)(-sint)=-6sintcost -> dt/dx = -1/6*sect*cosect
Thus dy/dx = 6sec^2(t) * (-1/6)*sect*cosect = -sec^3t*cosect, as required.
6. (Original post by the bear)
for part a) you divide dy/dt by dx/dt
(Original post by gdunne42)
Find dx/dt (and hence dt/dx) and dy/dt
Then dy/dx = dy/dt x dt/dx

Posted from TSR Mobile
That's a much quicker and nicer way of doing it, I'd never been taught to do it like that
7. (Original post by KaylaB)
That's a much quicker and nicer way of doing it, I'd never been taught to do it like that
the only sensible way ...
8. It's just using the fact that d/dx(f(g(x))=df(x)/dg(x)*dg(x)/dx
9. (Original post by constellarknight)
...
Full solutions are against forum guidelines, by the way.
10. (Original post by Zacken)
Full solutions are against forum guidelines, by the way.
Alright, whatever.
11. Im trying to dx/dt but I get -3(sin2t)
can someone explain the steps ? Sorry
12. (Original post by BroodiestPear)
Im trying to dx/dt but I get -3(sin2t)
can someone explain the steps ? Sorry
, so:

Which is basically the same thing as yours. It's just that it's easier to get the show that using the form above.
13. -3sin2t is an equivalent form of what I got, -6sintcost. It's just that it's easier to get to the required expression using -6sintcost.
14. Oh, I see it now Thanks for the help

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Updated: February 21, 2016
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