y R x O R Begin P = 5/4 - R x = R / & y =R / P8P(x, y, c) x < round (R / ) No Yes P= : Ta chon y i +1 = y i - Khi Pi +1 = Pi + (2x i + 3) + 4(1 - y i ) a 2b - Pi ( x , y ) = (0, b) ⇒ P0 = - 2b + a Begin P = 2(b*b)/(a*a)-2b+1 C1 = 2[(b*b)/(a*a)](2x+3) C2 = 2[(b*b)/(a*a)](2x+3) + 4(1-y) x=0&y=b P4P(x, y, c) b2 x × ≤1 a y No Yes P