( | 40 | + | x | − | 30 | ) | ( | 300 | − | 10 | x | ) | = | 3360 |
方程左边 = | 40 | ( | 300 | − | 10 | x | ) | + | x | ( | 300 | − | 10 | x | ) | − | 30 | ( | 300 | − | 10 | x | ) |
= | 40 | × | 300 | − | 40 | × | 10 | x | + | x | ( | 300 | − | 10 | x | ) | − | 30 | ( | 300 | − | 10 | x | ) |
= | 12000 | − | 400 | x | + | x | ( | 300 | − | 10 | x | ) | − | 30 | ( | 300 | − | 10 | x | ) |
= | 12000 | − | 400 | x | + | x | × | 300 | − | x | × | 10 | x | − | 30 | ( | 300 | − | 10 | x | ) |
= | 12000 | − | 100 | x | − | x | × | 10 | x | − | 30 | ( | 300 | − | 10 | x | ) |
= | 12000 | − | 100 | x | − | x | × | 10 | x | − | 30 | × | 300 | + | 30 | × | 10 | x |
= | 12000 | − | 100 | x | − | x | × | 10 | x | − | 9000 | + | 300 | x |
= | 3000 | + | 200 | x | − | x | × | 10 | x |
3000 | + | 200 | x | − | x | × | 10 | x | = | 3360 |