# Thread: 2 questions on parametric and implicit differntiations

1. ## 2 questions on parametric and implicit differntiations

Ok the curve has parametric equations:

x = cos t y = sin 2t, 0 ≤ t < 2pi

a) Find an expression for dy/dx in terms of parameter t
b) Find the values of the parameter t at the points where dy/dx = 0

An example in my book has confused me and so i was wondering if somebody could show me how to work through these two questions.
Thanks

2. Originally Posted by sharp357
the curve has parametric equations:

x = cos t y = sin 2t, 0 ≤ t < 2pi

a) Find an expression for dy/dx in terms of parameter t
b) Find the values of the parameter t at the points where dy/dx = 0

thanks
a) note that $\frac{dy}{dx} = \frac{\frac{dy}{dt}}{\frac{dx}{dt}}$

b) set $\frac{dy}{dx}$ found in (a) equal to 0 and solve for t.

3. Originally Posted by sharp357
Ok the curve has parametric equations:

x = cos t y = sin 2t, 0 ≤ t < 2pi

a) Find an expression for dy/dx in terms of parameter t
First find $y'$ then find $x'$ and to get $\tfrac{dy}{dx}$ form the fraction $\frac{y'}{x'}$.

b) Find the values of the parameter t at the points where dy/dx = 0
You want to solve $\frac{dy}{dx} = 0 \implies \frac{y'}{x'} = 0 \implies y' = 0$.
Can you finish?

4. ok i differentiated so dy/dx = cos 2t / - sin t

just wondering if this part is right?

5. $y = \sin(2t)$

chain rule ...

$\frac{dy}{dt} = 2\cos(2t)$

$\frac{dx}{dt} = -\sin{t}$ is correct