Sagot :
(3ab-2cd)(4ab+5cd)=12a²b²+15abcd-8abcd-10c²d²
=12a²b²+7abcd-10c²d²
=12a²b²+7abcd-10c²d²
[tex](3ab-2cd)(4ab+5cd) =\\\\=3ab\cdot 4ab+3ab\cdot 5cd-2cd\cdot 4ab-2cd\cdot 5cd=\\\\=12a^2b^2 +15ab cd-8abcd -10c^2d ^2=\\\\=12a^2b^2 +7abcd -10c^2d ^2[/tex]