| ( | X | − | 147 20 | ) | ( | X | − | 147 20 | ) | = | X | X | − | 400 |
| Left side of the equation = | X | ( | X | − | 147 20 | ) | − | 147 20 | ( | X | − | 147 20 | ) |
| = | X | X | − | X | × | 147 20 | − | 147 20 | ( | X | − | 147 20 | ) |
| = | X | X | − | 147 20 | X | − | 147 20 | X | + | 147 20 | × | 147 20 |
| = | X | X | − | 147 20 | X | − | 147 20 | X | + | 21609 400 |
| = | X | X | − | 147 10 | X | + | 21609 400 |
| X | X | − | 147 10 | X | + | 21609 400 | = | X | X | − | 400 |