| ( | a | − | 28 | ) | ( | 4 | + | 2 | ( | 40 | − | a | ) | ) | = | 96 |
| 方程左边 = | a | ( | 4 | + | 2 | ( | 40 | − | a | ) | ) | − | 28 | ( | 4 | + | 2 | ( | 40 | − | a | ) | ) |
| = | a | × | 4 | + | a | × | 2 | ( | 40 | − | a | ) | − | 28 | ( | 4 | + | 2 | ( | 40 | − | a | ) | ) |
| = | 4 | a | + | a | × | 2 | × | 40 | − | a | × | 2 | a | − | 28 | ( | 4 | + | 2 | ( | 40 | − | a | ) | ) |
| = | 4 | a | + | a | × | 80 | − | a | × | 2 | a | − | 28 | ( | 4 | + | 2 | ( | 40 | − | a | ) | ) |
| = | 84 | a | − | a | × | 2 | a | − | 28 | ( | 4 | + | 2 | ( | 40 | − | a | ) | ) |
| = | 84 | a | − | a | × | 2 | a | − | 28 | × | 4 | − | 28 | × | 2 | ( | 40 | − | a | ) |
| = | 84 | a | − | a | × | 2 | a | − | 112 | − | 56 | ( | 40 | − | a | ) |
| = | 84 | a | − | a | × | 2 | a | − | 112 | − | 56 | × | 40 | + | 56 | a |
| = | 84 | a | − | a | × | 2 | a | − | 112 | − | 2240 | + | 56 | a |
| = | 140 | a | − | a | × | 2 | a | − | 2352 |
| 140 | a | − | a | × | 2 | a | − | 2352 | = | 96 |