| t | t | + | ( | 21 | − | t | ) | ( | 21 | − | t | ) | = | 100 |
| Left side of the equation = | t | t | + | 21 | ( | 21 | − | t | ) | − | t | ( | 21 | − | t | ) |
| = | t | t | + | 21 | × | 21 | − | 21 | t | − | t | ( | 21 | − | t | ) |
| = | t | t | + | 441 | − | 21 | t | − | t | ( | 21 | − | t | ) |
| = | t | t | + | 441 | − | 21 | t | − | t | × | 21 | + | t | t |
| = | t | t | + | 441 | − | 42 | t | + | t | t |
| t | t | + | 441 | − | 42 | t | + | t | t | = | 100 |