| AD |
| DB |
| AE |
| EC |
∴
| AD |
| AB |
| AE |
| AC |
又∵∠A=∠A，
∴△ADE∽△ABC，
∴∠ADE=∠B，∴DE∥BC，
∴
| AB |
| DB |
| AC |
| EC |
（2）∵AC=3，EC=1，
∴AE=AC-EC=2，
∴
| AD |
| DB |
| AE |
| EC |
∴
| S△ACD |
| S△BCD |
| AD |
| BD |
∴S△ACD=2S△BCD，
∵S△ABC=S△ACD+S△BCD=3S△BCD，
∴
| S△ABC |
| S△BCD |
| AD |
| DB |
| AE |
| EC |
| AB |
| DB |
| AC |
| EC |
| S△ABC |
| S△BCD |
| AD |
| DB |
| AE |
| EC |
| AD |
| AB |
| AE |
| AC |
∴∠ADE=∠B，| AB |
| DB |
| AC |
| EC |
| AD |
| DB |
| AE |
| EC |
| S△ACD |
| S△BCD |
| AD |
| BD |
| S△ABC |
| S△BCD |