$a)_{}$ $4x^2+1-4x_{}$
$=4x^2-4x+1_{}$
$=(2x-1)^2_{}$
$b)_{}$ $x^2-y^2+2x+2y_{}$
$=(x-y)(x+y)+x+y_{}$
$=(x+y)(x-y+1)_{}$
$c)_{}$ $x^2-y^2+4y-4_{}$
$=x^2-(y^2-4y+4)_{}$
$=x^2-(y-2)^2_{}$
$= [ x-(y-2)]. [ x+(y-2)]_{}$
$=(x-y+2)(x+y-2)_{}$
$d)_{}$ $(x^2-2xy)^2-2.(x^2-2xy).y^2+y^4_{}$
$=(x^2-2xy)^2-2y^2.(x^2-2xy)+y^4_{}$
$=(x^2-2xy-y^2)^2_{}$
$e)_{}$ $x^2-4x-5_{}$
$=x^2+x-5x-5_{}$
$=x.(x+1)-5.(x+1)_{}$
$=(x+1)(x-5)_{}$
$f)_{}$ $x^2+3x+2_{}$
$=x^2+2x+x+2_{}$
$=x.(x+2)+(x+2)_{}$
$=(x+1)(x+2)_{}$
$g)_{}$ $x^4+4y^4_{}$
$=(x^2)^2+(2y^2)^2_{}$
$=(x^2)^2+4x^2y^2+(2y^2)^2-4x^2y^2_{}$
$=(x^2+y^2)^2-(2xy)^2_{}$
$=(x^2+2y^2-2xy).(x^2+2y^2+2xy)_{}$
$(x^2-1)^2-2y.(x-1)+y^2_{}$ ( sai đề hay sao ấy ).
