Cho tam giác ABC. Gọi I là điểm trên đoạn BC sao cho IB=3IC. Chứng minh: AL=3/4 AC-1/4AB.

* giải giúp mình cái này với ạ:

I. Supply the correct form of the verbs in brackets.

1. We (not see)..........them for a long time.

2. Listen! I (hear).........someone knocking at the door.

3.we (not receive)......... any letter since he (leave)......... 4 months before.

4.he (sleep).....in his room now.

5.where you (spend)....your holidays next summer?

6.violets (bloom).....in spring.

7.tom (not come)........here tomorrow.

8.my parents usually (hve)....tea for his breakfast.

9.they (prepare)...... the christmas dinner at the moment.

11. She (come)..........as soon as she (finish) her work.

12.george (work)...........at the university so far.

13.at present they (travel)......... to new york.

14. Look! The car ( go).........so fast.

15.my mother often ( teach)............me english on saturday evenings.