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# c3 parametric equations watch

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1. Can anyone answer this quest

x= cost y= sin2t 0<t<2pie
a) How express dy/dx in terms of t
b) Values of parameter t at points where dy/dx=0
c) Exact points of curve where tangents are parallel to x axis
d) Show cartesian equation for part of curve 0<t<pie is y= 2xsqrt(1-x)^2

Thanks
2. x = cos(t)
y = sin(2t)

dy/dt = 2cos2t

dx/dt = -sint
dt/dx = -1/sint

a)

dy/dx = dy/dt * dt/dx = 2cos2t * -1/sint = -2cos2t/sint

b)

-2cos2t/sint = 0
cos2t = 0
t = pi/4, 3pi/4, 5pi/4, 7pi/4

c)

plug values above in.

d)
3. (Original post by chewwy)
x = cos(t)
y = sin(2t)

dy/dt = 2cos2t

dx/dt = -sint
dt/dx = -1/sint

a)

dy/dx = dy/dt * dt/dx = 2cos2t * -1/sint = -2cos2t/sint

b)

-2cos2t/sint = 0
cos2t = 0
t = pi/4, 3pi/4, 5pi/4, 7pi/4

c)

plug values above in.

d)
thanks could you do part c more slowly?
4. (Original post by evapatel)
thanks could you do part c more slowly?
you just put the values you got for t in part b) into the equations you were given at the start (x=cos(t), y=sin(2t)), and you have the points where the line is parallel to the axis (because dy/dx = 0). hope that helps!
5. (Original post by pratikv)
you just put the values you got for t in part b) into the equations you were given at the start (x=cos(t), y=sin(2t)), and you have the points where the line is parallel to the axis (because dy/dx = 0). hope that helps!
Thankss
6. (Original post by evapatel)
Thankss
no worries. by the way, did you manage to get your halls sorted?
7. (Original post by pratikv)
no worries. by the way, did you manage to get your halls sorted?
We haven't been given the accomodation forms yet i was jus wonderin b4 wich ones wer good an i thought we could choose but i realised after you told me that you don't get to choose where you go an u have preferences like location. o wel i'l jus end up wer luck takes me. Thanks 4 ur help neway
8. (Original post by evapatel)
We haven't been given the accomodation forms yet i was jus wonderin b4 wich ones wer good an i thought we could choose but i realised after you told me that you don't get to choose where you go an u have preferences like location. o wel i'l jus end up wer luck takes me. Thanks 4 ur help neway
no worries. hopefully i'll see you round next year.

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