| 84 | − | x | + | 84 | + | ( | 180 | − | x | ) | ÷ | 2 | = | 180 |
| 方程左边 = | 168 | − | x | + | ( | 180 | − | x | ) | × | 1 2 |
| 168 | − | x | + | ( | 180 | − | x | ) | × | 1 2 | = | 180 |
| 方程左边 = | 168 | − | x | + | 180 | × | 1 2 | − | x | × | 1 2 |
| = | 168 | − | x | + | 90 | − | x | × | 1 2 |
| = | 258 | − | 3 2 | x |
| 258 | − | 3 2 | x | = | 180 |
| - | 3 2 | x | = | 180 | − | 258 |
| - | 3 2 | x | = | - | 78 |
| 78 | = | 3 2 | x |
3 2 | x | = | 78 |
| x | = | 78 | ÷ | 3 2 |
| = | 78 | × | 2 3 |
| = | 26 | × | 2 |
| x | = | 52 |