a/ Tam giác AMN cân tại A (gt). \(\Rightarrow\) \(\widehat{AMN}=\widehat{ANM};AM=AN.\)

Xét tam giác AMB và tam giác ANC có:

+ AM = AN (cmt).

+ \(\widehat{AMB}=\widehat{ANC}\left(\widehat{AMN}=\widehat{ANM}\right).\)

+ MB = NC (gt).

\(\Rightarrow\) Tam giác AMB = Tam giác ANC (c - g - c).

\(\Rightarrow\) AB = AC (cặp cạnh tương ứng).

Xét tam giác ABC có: AB = AC (cmt).

\(\Rightarrow\) Tam giác ABC cân tại A.

b/ Tam giác ABC cân tại A (cmt) \(\Rightarrow\) \(\widehat{ABC}=\widehat{ACB}.\)

Mà \(\widehat{ABC}=\widehat{MBH;}\widehat{ACB}=\widehat{NCK}\text{​​}\) (đối đỉnh).

\(\Rightarrow\) \(\widehat{MBH}=\widehat{NCK}.\)

Xét tam giác MBH và tam giác NCK \(\left(\widehat{BHM}=\widehat{CKN}=90^o\right)\)có:

+ MB = NC (gt).

+ \(\widehat{MBH}=\widehat{NCK}\left(cmt\right).\)

\(\Rightarrow\) Tam giác MBH = Tam giác NCK (cạnh huyền - góc nhọn).

c/ Tam giác MBH = Tam giác NCK (cmt).

\(\Rightarrow\) \(\widehat{BMH}=\widehat{CNK}\) (cặp góc tương ứng).

Xét tam giác OMN có: \(\widehat{NMO}=\widehat{MNO}\) (do \(\widehat{BMH}=\widehat{CNK}\)).

\(\Rightarrow\) Tam giác OMN tại O.

The doctor (already, examine)____________________ the patient.

Marconi (invent)________________ the telephone.

How many French tourists (meet)_______ she __________ last weekend?

They (repair)________________ their house all this month.

You (work)______________ too hard! That’s why you are tired.

When the doorbell (ring)_________, I (get)______ up and (answer)________it.

We (know)______________ her for years.

Her parents (live)__________ in Hue from 1985 to 1996.

The plant I bought (grow)______________ very much. And I water it every day.

We (meet)_________________ at 10 o’clock tonight.

Kate looks much thinner. She (lose)_____________ a lot of weight.

Look at those black clouds! It (rain)______________________.

Look! The fire engine (arrive)_________________.

Run! The bus driver (wait)_________________ for us!

Watch the baby! He (fall)__________________ off the bed.

Look at the sun! It (be)__________________ a very hot day!

It’s 7:30 in the morning and Mr. Brown (drive)_______________ to work, as usual.

Hurry up! We (miss)______________________ the train.

I (brush)_____________________ my teeth, have a wash and go to bed.

I (not have)_________________ breakfast this morning.

1 A

2 B

3 B

4 D

5 C

6 D

7 C

8 C

9 A

10 D

11 C

12 B

13 D

14 A

15 A

16 B