Ta có : 12.9+2.12-12

           = 12.(9+2)-12

            = 12.11 -12

             =132-12= 120

1. Does David live in the countryside in Canada?

⇒ Yes, he does. He lives in the countryside in Canada.

2. What does he usually do in the morning?

⇒ He usually gets up early and does morning exercise with his bike.

3. How does he go to school?

⇒ He goes to school by bus.

4. Does he have lessons from 9.00 am to 2.00 pm?

⇒ No, he doesn't. He has lessons from 9.00 am to 1.00 pm.

5. Where does he have lunch?

⇒ He often has lunch in the school canteen.

10+10+10

=30

S= \(1+3^2+...+3^{119}\)

=> 3S=\(3+3^2+...+3^{120}\)

=> 2S =\(3^{120}-1\)

\(S=\frac{3^{120}-1}{2}\)

Phải biết tập hợp A có bao nhiêu phần tử mới giải được bạn ạ.