Mn có cách nào để học tốt tiếng anh k ạ ? 

Hi Huy.

My name is Hieu.

Today, I would like to introduce to you some interesting and attractive places. Since I have a corona virus that infects everyone, I will send this to help you experience Hanoi city. There, you will experience Hanoi's specialties such as beef noodle soup, .. ... After eating you should go to visit famous places of Hanoi such as One Pillar Pagoda, Temple of Literature, .... This is a very sacred place, it is also a very meaningful place. with Vietnam. How do you feel about this place? Come visit them. Hope you have a nice trip.

Hieu

`x^2 - 2x + 8 < 0`

`<=> (x-1)^2 + 7 < 0`

`<=> (x-1)^2 < -7`

Vì `(x-1)^2 > -7` với mọi `x`

`=>` vô nghiệm 

Vậy `x \in RR`