| ( | n | + | 1 | − | 2 | ) | ÷ | 180 | = | ( | n | − | 2 | ) | ÷ | 180 | ÷ | 11 10 |
| Left side of the equation = | n | × | 1 180 | + | 1 | × | 1 180 | − | 2 | × | 1 180 |
| = | n | × | 1 180 | + | 1 180 | − | 1 90 |
| = | 1 180 | n | − | 1 180 |
1 180 | n | − | 1 180 | = | ( | n | − | 2 | ) | ÷ | 180 | ÷ | 11 10 |
| Right side of the equation = | ( | n | − | 2 | ) | × | 1 198 |
1 180 | n | − | 1 180 | = | ( | n | − | 2 | ) | × | 1 198 |
| Right side of the equation = | n | × | 1 198 | − | 2 | × | 1 198 |
| = | n | × | 1 198 | − | 1 99 |
1 180 | n | − | 1 180 | = | 1 198 | n | − | 1 99 |
1 180 | n | − | 1 198 | n | = | - | 1 99 | + | 1 180 |
1 1980 | n | = | - | 1 99 | + | 1 180 |
1 1980 | n | = | - | 1 220 |
| n | = | - | 1 220 | ÷ | 1 1980 |
| = | - | 1 220 | × | 1980 |
| = | - | 1 | × | 9 |
| n | = | - | 9 |