Lời giải:
b. $x^2-9-(x-3)(5-2x)=(x-3)(x+3)-(x-3)(5-2x)$
$=(x-3)[(x+3)-(5-2x)]=(x-3)(3x-2)$
d.
$5x(x-1)-3(x-1)=(x-1)(5x-3)$
f.
$x^3-x+3x^2y+3xy^2+y^3-y$
$=(x^3+y^3)-(x+y)+(3x^2y+3xy^2)$
$=(x+y)(x^2-xy+y^2)-(x+y)+3xy(x+y)$
$=(x+y)[(x^2-xy+y^2)-1+3xy]=(x+y)(x^2+2xy+y^2-1)$
$=(x+y)[(x+y)^2-1]=(x+y)(x+y-1)(x+y+1)$
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