Đáp án+Giải thích các bước giải:
$1)$ $2x(-2x-5)=(-2x.2x)+(-5.2x)=-4x^{2}+(-10x)=-4x^{2}-10x$
$2)$ $3x^{2}(2x-2)=(3x^{2}.2x)+[3x^{2}.(-2)]=6x^{3}+(-6x^{2})=6x^{3}-6x^{2}$
$3)$ $4x(-x-5)=[4x.(-x)]+[4x.(-5)]=-4x^{2}+(-20x)=-4x^{2}-20x$
$4)$ $-5x(-x+3)=[-5x.(-x)]+(-5x.3)=5x^{2}+(-15x)=5x^{2}-15x$
$5)$ $-6x(-x+7)=[-6x.(-x)]+(-6x.7)=6x^{2}+(-42x)=6x^{2}-42x$
$6)$ $-5x(-3x+4)=[-5x.(-3x)]+(-5x.4)=15x^{2}+(-20x)=15x^{2}-20x$
$7)$ $-4x^{3}(2x-1)=[-4x^{3}.2x)]+[(-4x^{3}.(-1)]=-8x^{4}+4x^{3}$
$8)$ $2x(-2x-3)=[2x.(-2x)]+[2x.(-3)]=-4x^{2}+(-6x)=-4x^{2}-6x$
$9)$ $-3x^{5}(4x-2)=(-3x^{5}.4x)+[-3x^{5}.(-2)]=-12x^{6}+6x^{5}$
$10)$ $-7x(2x+1)=(-7x.2x)+(-7x.1)=-14x^{2}-7x=-14x^{2}-7x$
