a) \(1.2.3....9-1.2.3...8-1.2.3...7.8^2\)
\(=1.2.3....8.\left(9-1-8\right)\)
\(=1.2.3...8.0\)
\(=0\)
1 . 1.3 ...9 - 1 . 2. 3...8 - 1.2.3...7.8 mũ 2
= 1.2.3...8. ( 9-1-8)
= 1.2.3...8.0
=0
Ta có 1.2.3...9 - 1.2.3...8 - 1.2.3...7.\(8^2\)
=1.2.3.4.5.6.7.8.(9-1-8)
=1.2.3.4.5.6.7.8.9.0=0