( | a | − | 18 | ) | ( | 320 | − | 10 | a | ) | = | 400 |
Left side of the equation = | a | ( | 320 | − | 10 | a | ) | − | 18 | ( | 320 | − | 10 | a | ) |
= | a | × | 320 | − | a | × | 10 | a | − | 18 | ( | 320 | − | 10 | a | ) |
= | 320 | a | − | a | × | 10 | a | − | 18 | × | 320 | + | 18 | × | 10 | a |
= | 320 | a | − | a | × | 10 | a | − | 5760 | + | 180 | a |
= | 500 | a | − | a | × | 10 | a | − | 5760 |
500 | a | − | a | × | 10 | a | − | 5760 | = | 400 |