Eliminating parameter to find a cartesian equation and sketching the curve

Question

x=sin(1/2)thetha , y=cos(1/2)thetha , -pi≤thetha≤pi 

 

What does the the negative interval mean ? And what does it mean when the angle is half ? 

Answer 1

x² + y² = 1 would be a unit circle but the restriction that -pi/2 ≤ θ ≤ pi/2 would restrict the graph to be that part of the circle in Quadrants IV & I.