... cú 1/ k 1/ k 1 1 f x1 , y1 = =11 k k xk , yk = k , k ữ ( 0,0 ) 1/ k 1/ k + ( 1/ k 1/ k ) nhng 1 1/ k 1/ k 1 2 x ,y = , f x2 , y = = ữ ( 0;0 ) k k k k k k 5 1/ k 1/ k ... Do k , ta cú 1 1/ k 1/ k 1 xk , yk = , ữ ( 0,0 ) f x1 , y1 = =00 k k k k 1/ k + 1/ k nhng 2 f x , y = / k 1/ k = x , y = , ( 0;0 ) ữ k k k k k k / k + 1/ k ( ) ( ) ( ... x y ) a) Do k , ta cú 1 1 1/ k 1 1 xk , yk = k , k ữ ( 0,0 ) f xk , yk = 1/ k + 1/ k = nhng 1/ k 2 2 f x ,y = x , y = , ( 0;0 ) = k k ữ k k 1/ k + / k k k ( ) ( )...