исследовать и построить график функции y=3x+x^3-3x^2

Rewrite the sentences with have to,don't have to and mustn't .

1)It isn't necessary for you to come ,but you can if you want to.

 You______________________________________

2)We aren't allowed to stay in the classroom at lunchtime.

 We________________________________________

3)It doesn't matter if you don't finish your dinner.

  You______________________________________

Помогите* Скласти у публицистичному стилі твір на тему: "Молодь та культура мовлення"