(x^2+1)(x-1)
<=> x-1=0 ( vì x^2+1 >= 1> 0 với mọi x)
<=> x= 1
Vậy x= 1

1. You don't have to pick me up tomorrow. I will take a taxi.

2. Look at that sign! You mustn't walk on the grass.

3. You mustn't blame anyone for your mistakes. You need to be responsible for yourself. 

4. You don't have to be absent from class tomorrow because the teacher will check your attendance 

5. I don't have to prepare dinner because we will eat out tonight. 

6. You mustn't  leave any rubbish here. It is forbidden.

7. You don't have to let anyone know that. It is a big secret.

8. You don't have to come early tomorrow because the event will start late.

9. You mustn't park your car here. There is a "No Parking" sign.