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# C3 parametric watch

1. x = 4t + cos2t
y= sin3t
show that dy/dx = 1/√2 when t=π/12

my dx/dt = 4 - 2sin2t
dt/dx = 1/ (4 - 2sin2t)

dy/dt = 3cos3t

so dy/dx= (3cos3t)/(4-2sin2t)

even substituting in π/12 gets me nowhere. the only thing i can possibly take out from the dy/dx is cos/sin = 1/tan and then im lost.
2. (Original post by ihatePE)
x = 4t + cos2t
y= sin3t
show that dy/dx = 1/√2 when t=π/12

my dx/dt = 4 - 2sin2t
dt/dx = 1/ (4 - 2sin2t)

dy/dt = 3cos3t

so dy/dx= (3cos3t)/(4-2sin2t)

even substituting in π/12 gets me nowhere. the only thing i can possibly take out from the dy/dx is cos/sin = 1/tan and then im lost.
just substitute in π/12 for t & make sure your calculator is in radians....

remember sin π/6 = 1/2

cos π/4 = 1/√2
3. (Original post by ihatePE)
...

even substituting in π/12 gets me nowhere
Why...?

You do know that , right? Or did you not enter stuff into your calc correctly?
4. (Original post by the bear)
just substitute in π/12 for t & make sure your calculator is in radians....

remember sin π/6 = 1/2

cos π/4 = 1/√2
i completely forgot about that, c2 is so far away
5. (Original post by RDKGames)
Why...?

You do know that , right? Or did you not enter stuff into your calc correctly?
i dont get it, how does
6. (Original post by ihatePE)
i dont get it, how does
From C1 you (should) know that . And . Divide one by the other and the indices subtract leaving you with which is 1/root2
7. (Original post by ihatePE)
i dont get it, how does
(Original post by RDKGames)
From C1 you (should) know that . And . Divide one by the other and the indices subtract leaving you with which is 1/root2
in other words and i'm sure you can do the rest
8. (Original post by will'o'wisp2)
in other words and i'm sure you can do the rest
that is if i wanted to rationalise the surd. here it asked me to reverse that which i never thought about before.

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