| ( | 8 | + | 2 | x | ) | ( | 5 | + | 2 | x | ) | = | 70 |
| 方程左边 = | 8 | ( | 5 | + | 2 | x | ) | + | 2 | x | ( | 5 | + | 2 | x | ) |
| = | 8 | × | 5 | + | 8 | × | 2 | x | + | 2 | x | ( | 5 | + | 2 | x | ) |
| = | 40 | + | 16 | x | + | 2 | x | ( | 5 | + | 2 | x | ) |
| = | 40 | + | 16 | x | + | 2 | x | × | 5 | + | 2 | x | × | 2 | x |
| = | 40 | + | 16 | x | + | 10 | x | + | 4 | x | x |
| = | 40 | + | 26 | x | + | 4 | x | x |
| 40 | + | 26 | x | + | 4 | x | x | = | 70 |
| x1= | - | 15 2 |
| x2=1 |