| 200 | ( | 1 | + | a% | ) | × | 9 | ÷ | 10 | × | 150 | ( | 1 | − | a% | ) | = | 20000 |
| 方程左边 = | 27000 | ( | 1 | + | a% | ) | ( | 1 | − | a% | ) |
| 27000 | ( | 1 | + | a% | ) | ( | 1 | − | a% | ) | = | 20000 |
| 方程左边 = | 27000 | × | 1 | ( | 1 | − | a% | ) | + | 27000 | × | a% | ( | 1 | − | a% | ) |
| = | 27000 | ( | 1 | − | a% | ) | + | 270 | a | ( | 1 | − | a% | ) |
| = | 27000 | × | 1 | − | 27000 | × | a% | + | 270 | a | ( | 1 | − | a% | ) |
| = | 27000 | − | 270 | a | + | 270 | a | ( | 1 | − | a% | ) |
| = | 27000 | − | 270 | a | + | 270 | a | × | 1 | − | 270 | a | × | a% |
| = | 27000 | − | 270 | a | + | 270 | a | − | 27 10 | a | a |
| = | 27000 | − | 0 | a | − | 27 10 | a | a |
| 27000 | − | 27 10 | a | a | = | 20000 |
| a1= | - | √70000 √27 |
| a2= | √70000 √27 |