已知x的平方-4x+1=0,求x的4次方+x的-4次方的值

x²-4x+1=0
x-4+1/x=0
x+1/x=4
x^4+x^(-4)
=x^4+1/x^4
=(x^2+1/x^2)²-2
=[(x+1/x)²-2]²-2
=（16-2）²-2
=196-2
=194