| x | x | + | ( | 40 | − | 4 | x | ) | ( | 40 | − | 4 | x | ) | = | 58 |
| Left side of the equation = | x | x | + | 40 | ( | 40 | − | 4 | x | ) | − | 4 | x | ( | 40 | − | 4 | x | ) |
| = | x | x | + | 40 | × | 40 | − | 40 | × | 4 | x | − | 4 | x | ( | 40 | − | 4 | x | ) |
| = | x | x | + | 1600 | − | 160 | x | − | 4 | x | ( | 40 | − | 4 | x | ) |
| = | x | x | + | 1600 | − | 160 | x | − | 4 | x | × | 40 | + | 4 | x | × | 4 | x |
| = | x | x | + | 1600 | − | 160 | x | − | 160 | x | + | 16 | x | x |
| = | x | x | + | 1600 | − | 320 | x | + | 16 | x | x |
| x | x | + | 1600 | − | 320 | x | + | 16 | x | x | = | 58 |