| 180 | n | ( | n | − | 2 | ) | − | 180 | ( | n | − | 2 | ) | = | 1510 | n |
| Left side of the equation = | 180 | n | n | − | 180 | n | × | 2 | − | 180 | ( | n | − | 2 | ) |
| = | 180 | n | n | − | 360 | n | − | 180 | ( | n | − | 2 | ) |
| = | 180 | n | n | − | 360 | n | − | 180 | n | + | 180 | × | 2 |
| = | 180 | n | n | − | 360 | n | − | 180 | n | + | 360 |
| = | 180 | n | n | − | 540 | n | + | 360 |
| 180 | n | n | − | 540 | n | + | 360 | = | 1510 | n |