| ( | 7 2 | + | 2 | a | ) | ( | 7 2 | + | a | ) | = | 100 |
| 方程左边 = | 7 2 | ( | 7 2 | + | a | ) | + | 2 | a | ( | 7 2 | + | a | ) |
| = | 7 2 | × | 7 2 | + | 7 2 | a | + | 2 | a | ( | 7 2 | + | a | ) |
| = | 49 4 | + | 7 2 | a | + | 2 | a | ( | 7 2 | + | a | ) |
| = | 49 4 | + | 7 2 | a | + | 2 | a | × | 7 2 | + | 2 | a | a |
| = | 49 4 | + | 7 2 | a | + | 7 | a | + | 2 | a | a |
| = | 49 4 | + | 21 2 | a | + | 2 | a | a |
49 4 | + | 21 2 | a | + | 2 | a | a | = | 100 |
| a1= | - | 39 4 |
| a2= | 9 2 |