Đáp án:
$1) (x^2 +2x+1) = (x+1)^2 = (x+1)(x+1)$
$2) x^2 -2x +1 = (x-1)^2 = (x-1)(x-1)$
$3) x^2 -4xy +4y^2 = (x-2y)^2= (x-2y)(x-2y)$
$4) 4x^2 -4xy +y^2 = (2x-y)^2 = (2x-y)(2x-y)$
$5) x^2 +6x +9 = (x+3)^2 = (x+3)(x+3)$
$6) x^2 -6x +9 = (x-3)^2 = (x-3)(x-3)$
$7)x^2 +2xt +t^2 = (x+t)^2 = (x+t)(x+t)$
$8) x^2 -2xt +t^2 = (x-t)^2 = (x-t)(x-t)$
$9) -x^2 +4x -4 = -(x^2 -4x+4) = -(x-2)^2 = -(x-2)(x-2)$
$10) x^2+2xy +y^2 -t^2 +2zt - z^2 = (x+y)^2 - (t-z)^2 = (x+y+t-z)(x+y-t+z)$
