| ( | 40 | − | 2 | t | ) | ( | 40 | − | 2 | t | ) | + | t | t | = | 40 |
| Left side of the equation = | 40 | ( | 40 | − | 2 | t | ) | − | 2 | t | ( | 40 | − | 2 | t | ) | + | t | t |
| = | 40 | × | 40 | − | 40 | × | 2 | t | − | 2 | t | ( | 40 | − | 2 | t | ) | + | t | t |
| = | 1600 | − | 80 | t | − | 2 | t | ( | 40 | − | 2 | t | ) | + | t | t |
| = | 1600 | − | 80 | t | − | 2 | t | × | 40 | + | 2 | t | × | 2 | t | + | t | t |
| = | 1600 | − | 80 | t | − | 80 | t | + | 4 | t | t | + | t | t |
| = | 1600 | − | 160 | t | + | 4 | t | t | + | t | t |
| 1600 | − | 160 | t | + | 4 | t | t | + | t | t | = | 40 |