Đáp án:
$d) \dfrac{x^2}{x^4} +2x^2-3$
$=\dfrac{1}{x^2} +2x^2 -3$
$=\dfrac{1}{x^2} + \dfrac{2x^4}{x^2} -\dfrac{3x^2}{x^2}$
$=\dfrac{2x^4-3x^2+1}{x^2}$
$=\dfrac{2x^4-2x^2-x^2+1}{x^2}$
$=\dfrac{2x^2(x^2-1)-(x^2-1)}{x^2}$
$=\dfrac{(x^2-1)(2x^2-1)}{x^2}$
$=\dfrac{(x-1)(x+1)(2x^2-1)}{x^2}$