30、D：x^2+y^2<=x+y+1x^2-x+1/4+y^2-y+1/4<=1+1/4+1/4(x-1/2)^2+(y-1/2)^2<=3/2D是以(1/2,1/2)为圆心、以√6/2为半径的圆内（包括圆周上）
