18 25 | ( | 40 | + | 2 | x | ) | ( | 90 | + | 2 | x | ) | = | 90 | × | 40 |
| Left side of the equation = | 18 25 | × | 40 | ( | 90 | + | 2 | x | ) | + | 18 25 | × | 2 | x | ( | 90 | + | 2 | x | ) |
| = | 144 5 | ( | 90 | + | 2 | x | ) | + | 36 25 | x | ( | 90 | + | 2 | x | ) |
| = | 144 5 | × | 90 | + | 144 5 | × | 2 | x | + | 36 25 | x | ( | 90 | + | 2 | x | ) |
| = | 2592 | + | 288 5 | x | + | 36 25 | x | ( | 90 | + | 2 | x | ) |
| = | 2592 | + | 288 5 | x | + | 36 25 | x | × | 90 | + | 36 25 | x | × | 2 | x |
| = | 2592 | + | 288 5 | x | + | 648 5 | x | + | 72 25 | x | x |
| = | 2592 | + | 936 5 | x | + | 72 25 | x | x |
| 2592 | + | 936 5 | x | + | 72 25 | x | x | = | 90 | × | 40 |
| Right side of the equation = | 3600 |
| 2592 | + | 936 5 | x | + | 72 25 | x | x | = | 3600 |