1/ $(3x+5)(2x-7)\\=3x(2x-7)+5(2x-7)\\=6x^2-21x+10x-35\\=6x^2-11x-35$
Vậy $(3x+5)(2x-7)=6x^2-11x-35$
2/ $(-5x+2)(-3x-4)\\=-(5x-2).[-(3x+4)]\\=(5x-2)(3x+4)\\=5x(3x+4)-2(3x+4)\\=15x^2+20x-6x-8\\=15x^2+14x-8$
Vậy $(-5x+2)(-3x-4)=15x^2+14x-8$
3/ $(x-5)(4x-3)\\=x(4x-3)-5(4x-3)\\=4x^2-3x-20x+15\\=4x^2-23x+15$
Vậy $(x-5)(4x-3)=4x^2-23x+15$
4/ $(x^2-2x-1)(x-3)\\=x(x^2-2x-1)-3(x^2-2x-1)\\=x^3-2x^2-x-3x^2+6x+3\\=x^3-5x^2+5x+3$
Vậy $(x^2-2x-1)(x-3)=x^3-5x^2+5x+3$
6/ $(2x-1)(x^2-5x+3)\\=2x(x^2-5x+3)-1(x^2-5x+3)\\=2x^3-10x^2+6x-x^2+5x-3\\=2x^3-11x^2+11x-3$
Vậy $(2x-1)(x^2-5x+3)=2x^3-11x^2+11x-3$