| ( | a | + | 8 | ) | ( | 8 | − | a | ) | ÷ | 2 | = | 30 |
| Left side of the equation = | a | ( | 8 | − | a | ) | × | 1 2 | + | 8 | ( | 8 | − | a | ) | × | 1 2 |
| = | a | ( | 8 | − | a | ) | × | 1 2 | + | 4 | ( | 8 | − | a | ) |
| = | a | × | 8 | × | 1 2 | − | a | a | × | 1 2 | + | 4 | ( | 8 | − | a | ) |
| = | a | × | 4 | − | a | a | × | 1 2 | + | 4 | ( | 8 | − | a | ) |
| = | 4 | a | − | a | a | × | 1 2 | + | 4 | × | 8 | − | 4 | a |
| = | 4 | a | − | a | a | × | 1 2 | + | 32 | − | 4 | a |
| = | 0 | a | − | a | a | × | 1 2 | + | 32 |
| 0 | a | − | a | a | × | 1 2 | + | 32 | = | 30 |