x=2+3cost,则3cost = x-2
y=3sint-1,则3sint = y+1
则(3cost)^2+(3sint)^2=(x-2)^2+(y+1)^2=3^2=9
即 (x-2)^2+(y+1)^2=9 即为半径r=3,圆点为(2,-1)的圆