1.
a, $2xy(x^2+xy-8y^2)=2x^3y+2x^2y-16xy^3$
b, $(x-2)(3x^2-2x)=3x^3-2x^2-6x^2+4x=3x^3-8x^2+4x$
c, $(2x+1)(x-1)(3x+2)=(2x^2-x-1)(3x+2)=6x^3+4x^2-3x^2-2x-3x-2=6x^3+x^2-5x-2$
d, (hình)
e, $(x-y)(x+y)(x^2+y^2)(x^4+y^4)$
$=(x^2-y^2)(x^2+y^2)(x^4+y^4)$
$=(x^4-y^4)(x^4+y^4)$
$=x^8-y^8$
2.
a, $9x^2-49=0\Leftrightarrow x=\dfrac{49}{9}\Leftrightarrow x=\pm\dfrac{7}{3}$
b, $(x+1)(x+2)-(x+2)=0$
$\Leftrightarrow (x+1-1)(x+2)=0$
$\Leftrightarrow x(x+2)=0$
$\Leftrightarrow x=0; x=-2$
c, $3x^2+2x+x^2+2x+1-(4x^2-25)=0$
$\Leftrightarrow 4x^2+4x+1-4x^2+25=0$
$\Leftrightarrow 4x=-26$
$\Leftrightarrow x=-6,5$
