View attachment 101255
Mn rút gọn giúp mk câu này vs ạ. Làm câu a thôi ak
đặt x+ 1/x =a
=> x^2+ 1/x^2= a^2-2
=> x^4+ 1/x^4= a^4-4a^2+2
khi đó: [tex]\frac{a^4-(a^4-4a^2+2)-2}{a^4+a^2-2}.\frac{x^4+1999x^2+1}{2x^2}\\\\ =\frac{4a^2-4}{(a^2+2).(a^2-1)}.\frac{x^4+1999x^2+1}{2x^2}\\\\ =\frac{4.(a^2-1)}{(a^2+2).(a^2-1)}.\frac{x^4+1999x^2+1}{2x^2}\\\\ =\frac{4}{a^2+2}.\frac{x^4+1999x^2+1}{2x^2}\\\\ =\frac{4}{x^2+\frac{1}{x^2}-4}.\frac{x^4+1999x^2+1}{2x^2}\\\\ =\frac{4x^2}{x^4+1-4x^2}.\frac{x^4+1999x^2+1}{2x^2}\\\\ =\frac{2x^4+1999x^2+1}{x^4-4x^2+1}[/tex]