$$x = 4\sin \left( {{\pi \over 2} - \omega t} \right)$$

$$ = 4\cos (\omega t)$$

$$y = 4\sin (\omega t)$$

$$ \Rightarrow {x^2} + {y^2} = {4^2}$$

$$\Rightarrow$$ The particle is moving in a circular motion with radius of 4 m.