| ( | 1 | − | a | ) | ( | 200 | + | 500 | a | ) | − | 40 | = | 200 |
| 方程左边 = | 1 | ( | 200 | + | 500 | a | ) | − | a | ( | 200 | + | 500 | a | ) | − | 40 |
| = | 1 | × | 200 | + | 1 | × | 500 | a | − | a | ( | 200 | + | 500 | a | ) | − | 40 |
| = | 200 | + | 500 | a | − | a | ( | 200 | + | 500 | a | ) | − | 40 |
| = | 160 | + | 500 | a | − | a | ( | 200 | + | 500 | a | ) |
| = | 160 | + | 500 | a | − | a | × | 200 | − | a | × | 500 | a |
| = | 160 | + | 300 | a | − | a | × | 500 | a |
| 160 | + | 300 | a | − | a | × | 500 | a | = | 200 |
| a1= | 1 5 |
| a2= | 2 5 |