| 500 | ( | 1 | + | a | ) | ( | 1 | + | 2 | a | ) | + | 400 | ( | 1 | + | a | ) | = | 900 | ( | 1 | + | 20 | a | ÷ | 9 | ) |
| 方程左边 = | 500 | × | 1 | ( | 1 | + | 2 | a | ) | + | 500 | a | ( | 1 | + | 2 | a | ) | + | 400 | ( | 1 | + | a | ) |
| = | 500 | ( | 1 | + | 2 | a | ) | + | 500 | a | ( | 1 | + | 2 | a | ) | + | 400 | ( | 1 | + | a | ) |
| = | 500 | × | 1 | + | 500 | × | 2 | a | + | 500 | a | ( | 1 | + | 2 | a | ) | + | 400 | ( | 1 | + | a | ) |
| = | 500 | + | 1000 | a | + | 500 | a | ( | 1 | + | 2 | a | ) | + | 400 | ( | 1 | + | a | ) |
| = | 500 | + | 1000 | a | + | 500 | a | × | 1 | + | 500 | a | × | 2 | a | + | 400 | ( | 1 | + | a | ) |
| = | 500 | + | 1000 | a | + | 500 | a | + | 1000 | a | a | + | 400 | ( | 1 | + | a | ) |
| = | 500 | + | 1500 | a | + | 1000 | a | a | + | 400 | ( | 1 | + | a | ) |
| = | 500 | + | 1500 | a | + | 1000 | a | a | + | 400 | × | 1 | + | 400 | a |
| = | 500 | + | 1500 | a | + | 1000 | a | a | + | 400 | + | 400 | a |
| = | 900 | + | 1900 | a | + | 1000 | a | a |
| 900 | + | 1900 | a | + | 1000 | a | a | = | 900 | ( | 1 | + | 20 | a | ÷ | 9 | ) |
| 方程右边 = | 900 | × | 1 | + | 900 | × | 20 | a | ÷ | 9 |
| = | 900 | + | 2000 | a |
| 900 | + | 1900 | a | + | 1000 | a | a | = | 900 | + | 2000 | a |
| a2= | 1 10 |