若x方-3x=1,求x方+1/x方和x四次方+1/x四次方的值
问题描述：
若x方-3x=1,求x方+1/x方和x四次方+1/x四次方的值
答
x²-3x=1
x²-3x-1=0
除以x得 x-3-1/x=0
x-1/x=3
x²+1/x²
=(x-1/x)²+2
=3²+2
=11
x^4+1/x^4
=(x²+1/x²)²-2
=11²-2
=119