a: 

b: 

a: Xét ΔCAB có 
M là trung điểm của CB

MK//AB

Do đó K là trung điẻm của AC

Xét ΔCAB có

M là trung điểm của BC

MH//CA

Do đó: H là trng điểm của AB

b: Xét tứ giác AHMK có góc AHM=góc AKM=góc KAH=90 độ

nên AHMK là hình chữ nhật

1D
2C
3B
4A
5A

IK=AB+CD2=10+242=17(cm)

1.Today the sun shines,more brightly than yesterday.

Yesterday the sun shone less brightly than today.

2.This cake is more freshly made than that one.

That cake is less freshly made than this one.

3.Jane behaves more politely than his younger brother.

Jane's younger brother behaves less politely than Jane.

4.Teenagers act more violently these das than in the past.

 Teenagers in the past acted less violently than teenagers these days.

5.The doctor treats his patients less patiently than he should.

The doctor should treat his patients more patiently than he does.