Cho tam giác ABC vuông tại A có đường cao AH.Vẽ HE vuông AB,HF vuông AC

1) Cho biết AB=3 cm, AC=4 cm. Tính HB,HC,AH

2) Chứng minh AE.EB+AF.FC=AH^2

3) Chứng minh BE=BC.cos^3 B

4) Chứng minh BE.BA+CF.CA+2HB.HC=BC^2

mọi người kẻ hình và giải thích rõ giúp mình với ạ

1.I like this book because the book is interesting

=>Because of

1.The floor is usually cleaned after school

2.A small party is being prepared in the garden now

3.Their task has just been finished

4.Sai de

5.Lot of sweet was bought by my studen last Sunday

6.A new swimming pool near our school will be built next year

I,

1.Many rivers and lakes are poisoned.Factoríe produce waste and pour it into rivers and lakes.

=>Because

=>Because of

2.They provided food then cleared up the debris.

=>After they 

3.The local people have to use water from the polluted river.They don't have enough fresh water.

=>If

4.I'm not you,but I think you should recycle these plastic carrier bags.

=>If I

5.All flights had to be cancelled as a rerult of the pilots' sudden strike. (so)

=>

6.You have to keep quiet if you want to stay here.

=>She told me that

II,

1.Water pollution/contamination/bodies/water/such as/lakes/rivers/oceans/groundwater.

2.America/celebrate/Thanks giving Day/Forth Thursday/November/since 1864/?/

3.Scotland/famous/its rich culture/well/its amazing/natural beauty/./

4.The Statue/Liberty/New York/is/monument/which/symbolize/freedom/./