| - | 90 | + | x | + | 2 | ( | x | + | 1 | ) | + | 3 | ( | x | + | 3 | ) | + | 9 | + | 4 | ( | x | + | 5 | ) | + | 5 | ( | x | + | 6 | ) | = | 0 |
| 方程左边 = | - | 81 | + | x | + | 2 | ( | x | + | 1 | ) | + | 3 | ( | x | + | 3 | ) | + | 4 | ( | x | + | 5 | ) | + | 5 | ( | x | + | 6 | ) |
| - | 81 | + | x | + | 2 | ( | x | + | 1 | ) | + | 3 | ( | x | + | 3 | ) | + | 4 | ( | x | + | 5 | ) | + | 5 | ( | x | + | 6 | ) | = | 0 |
| 方程左边 = | - | 81 | + | x | + | 2 | x | + | 2 | × | 1 | + | 3 | ( | x | + | 3 | ) | + | 4 | ( | x | + | 5 | ) | + | 5 | ( | x | + | 6 | ) |
| = | - | 81 | + | x | + | 2 | x | + | 2 | + | 3 | ( | x | + | 3 | ) | + | 4 | ( | x | + | 5 | ) | + | 5 | ( | x | + | 6 | ) |
| = | - | 79 | + | 3 | x | + | 3 | ( | x | + | 3 | ) | + | 4 | ( | x | + | 5 | ) | + | 5 | ( | x | + | 6 | ) |
| = | - | 79 | + | 3 | x | + | 3 | x | + | 3 | × | 3 | + | 4 | ( | x | + | 5 | ) | + | 5 | ( | x | + | 6 | ) |
| = | - | 79 | + | 3 | x | + | 3 | x | + | 9 | + | 4 | ( | x | + | 5 | ) | + | 5 | ( | x | + | 6 | ) |
| = | - | 70 | + | 6 | x | + | 4 | ( | x | + | 5 | ) | + | 5 | ( | x | + | 6 | ) |
| = | - | 70 | + | 6 | x | + | 4 | x | + | 4 | × | 5 | + | 5 | ( | x | + | 6 | ) |
| = | - | 70 | + | 6 | x | + | 4 | x | + | 20 | + | 5 | ( | x | + | 6 | ) |
| = | - | 50 | + | 10 | x | + | 5 | ( | x | + | 6 | ) |
| = | - | 50 | + | 10 | x | + | 5 | x | + | 5 | × | 6 |
| = | - | 50 | + | 10 | x | + | 5 | x | + | 30 |
| = | - | 20 | + | 15 | x |
| - | 20 | + | 15 | x | = | 0 |
| 15 | x | = | 0 | + | 20 |
| 15 | x | = | 20 |
| x | = | 20 | ÷ | 15 |
| = | 20 | × | 1 15 |
| = | 4 | × | 1 3 |
| x | = | 4 3 |
| x | = | 1.333333 |