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# C4 watch

1. How do you differentiate this, leaving it in terms of the parameter t ?

x= 4sin3t y=3cos3t
2. (Original post by kirstieluu)
How do you differentiate this, leaving it in terms of the parameter t ?

x= 4sin3t y=3cos3t
Are you trying to find ? Use the chain rule:

3. (Original post by tjf8)
dy/dx = dy/dt / dx/dt
dy/dx = d(3cos3t)/dt / d(4sin3t)/dt
dy/dx = -9sin3t/12cos3t
dy/dx = -3/4 tan3t

I think...
Posting full solutions is against the rules of this forum. Please try to guide towards an answer instead.
4. differentiation both
dy/dt and dx/dt

then write one over the other e.g. dy/dt over dx/dt (this is the same as dy/dx because the dt can cancel down)

write your solution on here and ill let you know if I agree (because we're not allowed to post solutions, only help you and check you've got it right/understand how to do it)
5. (Original post by notnek)
Posting full solutions is against the rules of this forum. Please try to guide towards an answer instead.
I was unaware of that – thank you.
6. Sorry, i wrote completely the wrong question.
I was meant to ask .. x=sect y=tant

Would you still use the chain rule on this? I got up to.. ?dy/dx= sec^t/sect tant

7. (Original post by kirstieluu)
Sorry, i wrote completely the wrong question.
I was meant to ask .. x=sect y=tant

Would you still use the chain rule on this? I got up to.. ?dy/dx= sec^t/sect tant

Yes the method is exactly the same and your working is correct.

You should be able to simplify from there.
8. (Original post by notnek)
Yes the method is exactly the same and your working is correct.

You should be able to simplify from there.
When i simplified it.. i got sec/tant
But the answer has got cosec in it and i dont know where that comes from?
9. (Original post by kirstieluu)
When i simplified it.. i got sec/tant
But the answer has got cosec in it and i dont know where that comes from?
Write sec and tan in terms of sin and cos.
10. (Original post by kirstieluu)
When i simplified it.. i got sec/tant
But the answer has got cosec in it and i dont know where that comes from?
I assume that you know that

And that you know how to divide by a fraction
11. (Original post by kirstieluu)
When i simplified it.. i got sec/tant
But the answer has got cosec in it and i dont know where that comes from?
In addition to TenOfThem's post, note that we define secant as follows

.

There's nothing "official" about this (it's just a man-made definition of 1 over cos t).
12. I've got sect/tant = sec/1 x cost/sint

Now I'm stuck
13. (Original post by kirstieluu)
I've got sect/tant = sec/1 x cost/sint

Now I'm stuck
What's

?
14. I get it now. Thanks for the help guys!

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