Point moves anticlockwise around circle x^2 + y^2 =1 at uniform speed of 2 m/s

a) Find expression for rates of change of its x - coordinate in terms of x, when the point is above the x -axis

My attempt:

Since v = 2,

Then dx/dt^2 + dy/dt^2 = v = 2

then dx/dt^2 = 2- dy/dt

Is that correct, cause the book has -2sqrt(1-x^2)