| ( | 30 | + | 3 | x | ) | ( | 28 | + | 2 | x | ) | = | 1152 |
| 方程左边 = | 30 | ( | 28 | + | 2 | x | ) | + | 3 | x | ( | 28 | + | 2 | x | ) |
| = | 30 | × | 28 | + | 30 | × | 2 | x | + | 3 | x | ( | 28 | + | 2 | x | ) |
| = | 840 | + | 60 | x | + | 3 | x | ( | 28 | + | 2 | x | ) |
| = | 840 | + | 60 | x | + | 3 | x | × | 28 | + | 3 | x | × | 2 | x |
| = | 840 | + | 60 | x | + | 84 | x | + | 6 | x | x |
| = | 840 | + | 144 | x | + | 6 | x | x |
| 840 | + | 144 | x | + | 6 | x | x | = | 1152 |