| ( | 2021 | − | x | ) | ( | 2020 | − | x | ) | = | 1 |
| Left side of the equation = | 2021 | ( | 2020 | − | x | ) | − | x | ( | 2020 | − | x | ) |
| = | 2021 | × | 2020 | − | 2021 | x | − | x | ( | 2020 | − | x | ) |
| = | 4082420 | − | 2021 | x | − | x | ( | 2020 | − | x | ) |
| = | 4082420 | − | 2021 | x | − | x | × | 2020 | + | x | x |
| = | 4082420 | − | 4041 | x | + | x | x |
| 4082420 | − | 4041 | x | + | x | x | = | 1 |