Haven't learnt inverse trig functions..
But it might be right.
-2(root[1-x^2])
Whoops haha it simplifies to that.
The first thing you have to do is get the parametric function:
x = cosø
dx/dt = -(dø/dt)sinø
dx/dt = -(dø/dt)√(1-x^2)
Then you have to work out dø/dt, which is angular velocity.
Given tangential velocity = 2 m/s
Period T = (2π)/2 = π
But you know angular velocity w = 2π/T
So w = 2π/π = 2 = dø/dt
ie. dx/dt = -2√(1-x^2)