Question

用换元法解方程X^4+X^2+1/X^4+1/X^2=4

Answer 1

x^4+1/x^4=(x^2+1/x^2)^2-2

设x^2+1/x^2=y

y^2-2+y-4=0

(y+3)(y-2)=0

y1=-3,y2=2

再分别讨论