Rút gọn phân thức: x^4 - 5x^2 +4 / x^4 -10x^2 + 9

x4−5x2+4x4−10x2+9=x4−4x2−x2+4x4−9x2−x2+9=x2x2−4−x2−4x2x2−9−x2−9=x2−4x2−1x2−9x2−1=x2−4x2−9