x^2-13x+1=0.x≠0.
x-13+1/x=0,
x+1/x=13.
(x+1/x)^2=169
x^2+1/x^2=169-2=167
(x^2+1/x^2)^2=167^2.
x^4+1/^4=167^2-2.
x^4+1/x^4=27887.