[tex]x(x-2009)-y(2009-x)\\=x(x-2009)+y(x-2009)\\=(x-2009)(x+y)\\Thay-vao\\(3009-2009)(3009+1991)\\=1000.5000\\=5000000[/tex]
[tex]x^2-y^2-2x+2y\\=(x+y)(x-y)-(2x-2y)\\=(x+y)(x-y)-2(x-y)\\=(x-y)(x+y+2)\\Thay-vao\\=(2345-2344)(2345+2344+2)\\=1.4691\\=4691[/tex]
Câu c coi lại đề chút, phải là: [tex]x^2{\color{Red} +}2009x-y^2+2009y[/tex]
PS: Hãy like khi mk đã giúp đỡ bn