a) Xét tam giác HFB và tam giác HEC có
góc BFH = góc CEH (1)
góc H chung(2)
Từ 1 và 2 => tam giác HFB đồng dạng tam giác HEC
b) B1: Chứng minh 2 tam giác BEA và tam giác BFH (có góc BEA = góc BFH, góc B chung)
=> BA/BH = BE/BF (Tỉ số đồng dạng)=> BA.BF=BH.BE

1. Where is the Great Wall?
-> The Great Wall is in China

2. When was it built?

-> The Great Wall of China was built from 246 - 209 BC

3. What is it made of?
The people of China made it to keep out their enemies

4. What was it built for?

-> The people of China made it to keep out their enemies. There are watch towers all along the way. The Wall is made of brick and earth. It is high and wide on top. People can walk along
the top as if it were a road. No other defense line has ever been made as long as the Great Wall of China.