| ( | 20 | − | 2 | x | ) | ( | 13 | − | 2 | x | ) | = | 144 |
| Left side of the equation = | 20 | ( | 13 | − | 2 | x | ) | − | 2 | x | ( | 13 | − | 2 | x | ) |
| = | 20 | × | 13 | − | 20 | × | 2 | x | − | 2 | x | ( | 13 | − | 2 | x | ) |
| = | 260 | − | 40 | x | − | 2 | x | ( | 13 | − | 2 | x | ) |
| = | 260 | − | 40 | x | − | 2 | x | × | 13 | + | 2 | x | × | 2 | x |
| = | 260 | − | 40 | x | − | 26 | x | + | 4 | x | x |
| = | 260 | − | 66 | x | + | 4 | x | x |
| 260 | − | 66 | x | + | 4 | x | x | = | 144 |
| x2= | 29 2 |