Bonsoir ;
[tex]-(5x-10)+(5x-10)(10x-3)=(5x-10)(-1+10x-3)\\\\ =(5x-10)(10x-4) .\\\\ \textit{On a : } 5x-10=5(x-2) \textit{ et } 10x-4 = 2(5x-2) \textit{ , donc :} \\\\ -(5x-10)+(5x-10)(10x-3)=10(x-2)(5x-2) .[/tex]
[tex]-36x^2 + 81 = -9(4x^2-9)=-9((2x)^2-3^2)\\\\ = -9(2x-3)(2x+3) : \textit{ c'est identit\'e remarquable .}[/tex]