| 20 | ( | 1 | + | y | ) | y | + | 40 | ( | 1 | + | 2 | y | ) | y | = | 20 | ( | 1 | + | y | ) | + | 40 | ( | 1 | + | 2 | y | ) | + | 100 |
| 方程左边 = | 20 | × | 1 | y | + | 20 | y | y | + | 40 | ( | 1 | + | 2 | y | ) | y |
| = | 20 | y | + | 20 | y | y | + | 40 | ( | 1 | + | 2 | y | ) | y |
| = | 20 | y | + | 20 | y | y | + | 40 | × | 1 | y | + | 40 | × | 2 | y | y |
| = | 20 | y | + | 20 | y | y | + | 40 | y | + | 80 | y | y |
| = | 60 | y | + | 20 | y | y | + | 80 | y | y |
| 60 | y | + | 20 | y | y | + | 80 | y | y | = | 20 | ( | 1 | + | y | ) | + | 40 | ( | 1 | + | 2 | y | ) | + | 100 |
| 方程右边 = | 20 | × | 1 | + | 20 | y | + | 40 | ( | 1 | + | 2 | y | ) | + | 100 |
| = | 20 | + | 20 | y | + | 40 | ( | 1 | + | 2 | y | ) | + | 100 |
| = | 120 | + | 20 | y | + | 40 | ( | 1 | + | 2 | y | ) |
| = | 120 | + | 20 | y | + | 40 | × | 1 | + | 40 | × | 2 | y |
| = | 120 | + | 20 | y | + | 40 | + | 80 | y |
| = | 160 | + | 100 | y |
| 60 | y | + | 20 | y | y | + | 80 | y | y | = | 160 | + | 100 | y |